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‎README.md

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![DSA Learning](https://img.shields.io/badge/DSA-Learning-blue?style=for-the-badge&logo=leetcode)
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This repository contains solutions for a couple hundred DSA problems from the [LeetCode](https://leetcode.com/)
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This repository contains solutions for 511 DSA problems from the [LeetCode](https://leetcode.com/)
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website.
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Problems are separated into 19 topics:
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| | Topic | Package |
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|---:|:--------------------|:-----------------------------------------------|
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| 1 | Array | [array](src/array) |
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| 2 | Binary | [binary](src/binary) |
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| 3 | Binary Search | [binary_search](src/binary_search) |
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| 4 | Binary Search Tree | [binary_search_tree](src/binary_search_tree) |
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| 5 | Binary Tree | [binary_tree](src/binary_tree) |
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| 6 | Design | [design](src/design) |
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| 7 | Dynamic Programming | [dynamic_programming](src/dynamic_programming) |
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| 8 | Graph | [graph](src/graph) |
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| 9 | Greedy Algorithms | [greedy](src/greedy) |
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| 10 | Heap | [heap](src/heap) |
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| 11 | Interval | [interval](src/interval) |
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| 12 | Linked List | [linked_list](src/linked_list) |
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| 13 | Math | [math](src/math) |
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| 14 | Matrix | [matrix](src/matrix) |
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| 15 | Quad Tree | [quad_tree](src/quad_tree) |
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| 16 | Recursion | [recursion](src/recursion) |
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| 17 | Stack | [stack](src/stack) |
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| 18 | String | [string](src/string) |
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| 19 | Trie | [trie](src/trie) |
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| | Topic | Package | Problems |
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|---:|:--------------------|:-----------------------------------------------|---------:|
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| 1 | Array | [array](src/array) | 69 |
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| 2 | Binary | [binary](src/binary) | 12 |
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| 3 | Binary Search | [binary_search](src/binary_search) | 18 |
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| 4 | Binary Search Tree | [binary_search_tree](src/binary_search_tree) | 16 |
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| 5 | Binary Tree | [binary_tree](src/binary_tree) | 45 |
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| 6 | Design | [design](src/design) | 17 |
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| 7 | Dynamic Programming | [dynamic_programming](src/dynamic_programming) | 45 |
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| 8 | Graph | [graph](src/graph) | 63 |
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| 9 | Greedy Algorithms | [greedy](src/greedy) | 20 |
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| 10 | Heap | [heap](src/heap) | 18 |
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| 11 | Interval | [interval](src/interval) | 11 |
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| 12 | Linked List | [linked_list](src/linked_list) | 31 |
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| 13 | Math | [math](src/math) | 19 |
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| 14 | Matrix | [matrix](src/matrix) | 18 |
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| 15 | Quad Tree | [quad_tree](src/quad_tree) | 1 |
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| 16 | Recursion | [recursion](src/recursion) | 24 |
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| 17 | Stack | [stack](src/stack) | 25 |
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| 18 | String | [string](src/string) | 54 |
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| 19 | Trie | [trie](src/trie) | 4 |
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## Good places to start your own LeetCode journey
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- [NeetCode](https://neetcode.io/) – organized roadmap, code solutions in 14 languages and video explanations
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- [Grind 75](https://www.techinterviewhandbook.org/grind75) – customizable study plan, algorithms cheetsheet and interview preparation guide
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- [Grind 75](https://www.techinterviewhandbook.org/grind75) – customizable study plan, algorithms cheatsheet and
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interview preparation guide
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## My LeetCode profile
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‎src/dynamic_programming/MaximumSubarray.java

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@@ -12,11 +12,7 @@ public int maxSubArrayViaKadaneAlgo(int[] nums) {
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int max = Integer.MIN_VALUE;
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int sum = 0;
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for (int num : nums) {
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sum += num;
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if (sum < num) {
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sum = num;
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}
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sum = Math.max(sum + num, num);
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max = Math.max(sum, max);
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}
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‎src/dynamic_programming/MaximumSumCircularSubarray.java

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package dynamic_programming;
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/**
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* Description: https://leetcode.com/problems/maximum-sum-circular-subarray
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* Difficulty: Medium
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* Time complexity: O(n)
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* Space complexity: O(1)
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*/
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public class MaximumSumCircularSubarray {
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public int maxSubarraySumCircularViaModifiedKadaneAlgo(int[] nums) {
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// we keep track of both minimum sum subarray and maximum size subarray
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int minSum = 0;
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int maxSum = 0;
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int totalSum = 0;
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int min = Integer.MAX_VALUE;
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int max = Integer.MIN_VALUE;
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for (int num : nums) {
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minSum = Math.min(minSum + num, num);
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maxSum = Math.max(maxSum + num, num);
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totalSum += num;
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min = Math.min(min, minSum);
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max = Math.max(max, maxSum);
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}
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// maximum sum circular subarray can either be in the middle of a regular array -> [min] [max] [min] -> max
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// or on both ends of it -> [max] [min] [max] -> totalSum - min
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return max > 0 ? Math.max(max, totalSum - min) : max;
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}
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}

‎src/string/OneEditDistance.java

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public boolean isOneEditDistance(String first, String second) {
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if (first.length() > second.length()) return isOneEditDistance(second, first);
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if (second.length() - first.length() > 2) return false;
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if (second.length() - first.length() > 1
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|| first.equals(second)) {
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return false;
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}
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boolean hasEdit = false;
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int i = 0;

‎src/string/StringJustification.java

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package string;
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import java.util.ArrayList;
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import java.util.List;
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/**
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* Description: https://leetcode.com/problems/text-justification
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* Difficulty: Hard
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* Time complexity: O(n)
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* Space complexity: O(n)
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*/
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public class StringJustification {
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public List<String> fullJustify(String[] words, int maxWidth) {
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List<String> justified = new ArrayList<>();
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List<String> currentLine = new ArrayList<>();
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int currentLineLength = 0;
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for (String word : words) {
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if (word.length() + currentLineLength + currentLine.size() <= maxWidth) {
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currentLine.add(word);
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currentLineLength += word.length();
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} else {
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justified.add(buildLine(currentLine, currentLineLength, false, maxWidth));
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currentLine = new ArrayList<>();
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currentLine.add(word);
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currentLineLength = word.length();
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}
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}
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justified.add(buildLine(currentLine, currentLineLength, true, maxWidth));
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return justified;
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}
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private String buildLine(List<String> words, int length, boolean isLastLine, int maxLength) {
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if (isLastLine || words.size() == 1) {
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return buildLeftJustifiedLine(words, length, maxLength);
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}
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return buildMidJustifiedLine(words, length, maxLength);
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}
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private String buildLeftJustifiedLine(List<String> words, int length, int maxLength) {
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StringBuilder line = new StringBuilder();
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for (int i = 0; i < words.size(); i++) {
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line.append(words.get(i));
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if (i < words.size() - 1) line.append(" ");
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}
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int extraSpaces = maxLength - length - (words.size() - 1);
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for (int i = 0; i < extraSpaces; i++) {
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line.append(" ");
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}
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return line.toString();
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}
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private String buildMidJustifiedLine(List<String> words, int length, int maxLength) {
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int spaces = maxLength - length;
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int evenSpaces = spaces / (words.size() - 1);
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int extraSpaces = spaces % (words.size() - 1);
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StringBuilder line = new StringBuilder();
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for (int i = 0; i < words.size(); i++) {
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line.append(words.get(i));
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if (i == words.size() - 1) break;
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for (int j = 0; j < evenSpaces; j++) {
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line.append(" ");
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}
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if (extraSpaces > 0) {
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line.append(" ");
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extraSpaces--;
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}
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}
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return line.toString();
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}
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}

‎src/string/SubstringWithConcatenationOfAllWords.java

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package string;
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import java.util.ArrayList;
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import java.util.HashMap;
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import java.util.List;
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import java.util.Map;
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/**
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* Description: https://leetcode.com/problems/substring-with-concatenation-of-all-words
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* Difficulty: Hard
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* Time complexity: O(w + (s - w * wl) * (w + w * wl))
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* Space complexity: O(w + wl)
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*/
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public class SubstringWithConcatenationOfAllWords {
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public List<Integer> findSubstring(String s, String[] words) {
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int wordLength = words[0].length();
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Map<String, Integer> freqMap = buildFreqMap(words);
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List<Integer> result = new ArrayList<>();
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for (int start = 0; start <= s.length() - words.length * wordLength; start++) {
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if (isMatch(s, words, wordLength, freqMap, start)) {
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result.add(start);
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}
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}
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return result;
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}
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private boolean isMatch(
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String s,
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String[] words,
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int wordLength,
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Map<String, Integer> freqMap,
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int start) {
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Map<String, Integer> freqMapCopy = new HashMap<>(freqMap);
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int found = 0;
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for (int i = 0; i < words.length; i++) {
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String word = s.substring(start + i * wordLength, start + i * wordLength + wordLength);
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int count = freqMapCopy.getOrDefault(word, 0);
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if (count <= 0) return false;
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freqMapCopy.merge(word, -1, Integer::sum);
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found += 1;
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if (found == words.length) return true;
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}
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return false;
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}
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private Map<String, Integer> buildFreqMap(String[] words) {
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Map<String, Integer> freqMap = new HashMap<>();
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for (String word : words) {
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freqMap.merge(word, 1, Integer::sum);
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}
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return freqMap;
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}
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}

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