Chapter 04 section 02 C++ codes updated. multiset codes added. Java codes added.

liuyubobobo · liuyubobobo · commit 81498621c04d · 2017-11-14T02:48:27.000-08:00
diff --git a/04-Using-Hash-Table/Course Code (C++)/02-Intersection-of-Two-Arrays-II/basic_map_main.cpp b/04-Using-Hash-Table/Course Code (C++)/02-Intersection-of-Two-Arrays-II/basic_map_main.cpp
@@ -7,36 +7,42 @@ using namespace std;
 int main() {
 
     map<int,int> myMap;
-    if( myMap.find( 42 ) == myMap.end() )
-        cout<<"Can not find element 42"<<endl;
+    if(myMap.find(42) == myMap.end())
+        cout << "Can not find element 42" << endl;
     else
-        cout<<"Element 42 is in the map"<<endl;
+        cout << "Element 42 is in the map" << endl;
 
-    cout<<myMap[42]<<endl;
-    if( myMap.find( 42 ) == myMap.end() )
-        cout<<"Can not find element 42"<<endl;
+    cout << myMap[42] << endl; // 输出 0
+
+    // 注意: 在C++中, map的key一旦被访问过, 就会添加默认的(key, value)对在map中!
+    // 以下代码将找到42, 因为之前使用myMap[42]的方式对42进行了访问!
+    if(myMap.find(42) == myMap.end())
+        cout << "Can not find element 42" << endl;
     else
-        cout<<"Element 42 is in the map"<<endl;
+        cout << "Element 42 is in the map" << endl;
 
     myMap[42] ++;
-    cout<<myMap[42]<<endl;
-    if( myMap.find( 42 ) == myMap.end() )
-        cout<<"Can not find element 42"<<endl;
+    cout << myMap[42] << endl; // 输出 1
+    if(myMap.find(42) == myMap.end())
+        cout << "Can not find element 42" << endl;
     else
-        cout<<"Element 42 is in the map"<<endl;
+        cout << "Element 42 is in the map" << endl;
 
     myMap[42] --;
-    cout<<myMap[42]<<endl;
-    if( myMap.find( 42 ) == myMap.end() )
-        cout<<"Can not find element 42"<<endl;
+    cout << myMap[42] << endl; // 输出 0
+
+    // 注意: key对应的值为0, 不代表key不存在
+    if(myMap.find(42) == myMap.end())
+        cout << "Can not find element 42" << endl;
     else
-        cout<<"Element 42 is in the map"<<endl;
+        cout << "Element 42 is in the map" << endl;
 
-    myMap.erase( 42 );
-    if( myMap.find( 42 ) == myMap.end() )
-        cout<<"Can not find element 42"<<endl;
+    // 使用erase删除一个key
+    myMap.erase(42);
+    if(myMap.find(42) == myMap.end())
+        cout << "Can not find element 42" << endl;
     else
-        cout<<"Element 42 is in the map"<<endl;
+        cout << "Element 42 is in the map" << endl;
 
     return 0;
 }
diff --git a/04-Using-Hash-Table/Course Code (C++)/02-Intersection-of-Two-Arrays-II/main.cpp b/04-Using-Hash-Table/Course Code (C++)/02-Intersection-of-Two-Arrays-II/main.cpp
@@ -9,13 +9,13 @@ class Solution {
     vector<int> intersect(vector<int>& nums1, vector<int>& nums2) {
 
         map<int, int> record;
-        for( int i = 0 ; i < nums1.size() ; i ++ )
+        for(int i = 0 ; i < nums1.size() ; i ++)
             record[nums1[i]] += 1;
 
         vector<int> resultVector;
-        for( int i = 0 ; i < nums2.size() ; i ++ )
-            if( record[ nums2[i] ] > 0 ){
-                resultVector.push_back( nums2[i] );
+        for(int i = 0 ; i < nums2.size() ; i ++)
+            if(record[nums2[i]] > 0){
+                resultVector.push_back(nums2[i]);
                 record[nums2[i]] --;
             }
 
@@ -32,9 +32,9 @@ int main() {
     vector<int> vec2(nums2, nums2 + sizeof(nums2)/sizeof(int));
 
     vector<int> res = Solution().intersect(vec1, vec2);
-    for(int i = 0 ; i < res.size() ; i ++ )
-        cout<<res[i]<<" ";
-    cout<<endl;
+    for(int i = 0 ; i < res.size() ; i ++)
+        cout << res[i] << " ";
+    cout << endl;
 
     return 0;
 }
diff --git a/04-Using-Hash-Table/Course Code (C++)/02-Intersection-of-Two-Arrays-II/main2.cpp b/04-Using-Hash-Table/Course Code (C++)/02-Intersection-of-Two-Arrays-II/main2.cpp
@@ -1,6 +1,7 @@
 #include <iostream>
 #include <vector>
 #include <map>
+
 using namespace std;
 
 /// 350. Intersection of Two Arrays II
@@ -9,20 +10,21 @@ class Solution {
     vector<int> intersect(vector<int>& nums1, vector<int>& nums2) {
 
         map<int, int> record;
-        for( int i = 0 ; i < nums1.size() ; i ++ )
-            if( record.find(nums1[i]) == record.end() )
-                record.insert( make_pair(nums1[i],1));
+        for(int i = 0 ; i < nums1.size() ; i ++)
+            if(record.find(nums1[i]) == record.end())
+                record.insert(make_pair(nums1[i],1));
             else
                 record[nums1[i]] += 1;
 
         vector<int> resultVector;
-        for( int i = 0 ; i < nums2.size() ; i ++ )
-            if( record.find(nums2[i]) != record.end() &&
-                record[ nums2[i] ] > 0 ){
-                resultVector.push_back( nums2[i] );
+        for(int i = 0 ; i < nums2.size() ; i ++)
+            if(record.find(nums2[i]) != record.end() &&
+               record[nums2[i]] > 0){
+
+                resultVector.push_back(nums2[i]);
                 record[nums2[i]] --;
-                if( record[nums2[i]] == 0 )
-                    record.erase( nums2[i] );
+                if(record[nums2[i]] == 0)
+                    record.erase(nums2[i]);
             }
 
         return resultVector;
@@ -38,9 +40,9 @@ int main() {
     vector<int> vec2(nums2, nums2 + sizeof(nums2)/sizeof(int));
 
     vector<int> res = Solution().intersect(vec1, vec2);
-    for(int i = 0 ; i < res.size() ; i ++ )
-        cout<<res[i]<<" ";
-    cout<<endl;
+    for(int i = 0 ; i < res.size() ; i ++)
+        cout << res[i] << " ";
+    cout << endl;
 
     return 0;
 }
diff --git a/04-Using-Hash-Table/Course Code (C++)/02-Intersection-of-Two-Arrays-II/main3.cpp b/04-Using-Hash-Table/Course Code (C++)/02-Intersection-of-Two-Arrays-II/main3.cpp
@@ -0,0 +1,44 @@
+#include <iostream>
+#include <vector>
+#include <set>
+
+using namespace std;
+
+/// 350. Intersection of Two Arrays II
+/// Using multiset
+class Solution {
+public:
+    vector<int> intersect(vector<int>& nums1, vector<int>& nums2) {
+
+        multiset<int> record;
+        for(int num: nums1)
+            record.insert(num);
+
+        multiset<int> result;
+        for(int num: nums2){
+            multiset<int>::iterator iter = record.find(num);
+            if( iter != record.end()){
+                result.insert(num);
+                record.erase(iter);
+            }
+        }
+
+        return vector<int>(result.begin(), result.end());
+    }
+};
+
+int main() {
+
+    int nums1[] = {1, 2, 2, 1};
+    vector<int> vec1(nums1, nums1 + sizeof(nums1)/sizeof(int));
+
+    int nums2[] = {2, 2};
+    vector<int> vec2(nums2, nums2 + sizeof(nums2)/sizeof(int));
+
+    vector<int> res = Solution().intersect(vec1, vec2);
+    for(int i = 0 ; i < res.size() ; i ++)
+        cout << res[i] << " ";
+    cout << endl;
+
+    return 0;
+}
diff --git a/04-Using-Hash-Table/Course Code (Java)/02-Intersection-of-Two-Arrays-II/src/Main.java b/04-Using-Hash-Table/Course Code (Java)/02-Intersection-of-Two-Arrays-II/src/Main.java
@@ -0,0 +1,55 @@
+/// 让我们来测试使用Java中的TreeMap:)
+
+import java.util.TreeMap;
+
+public class Main {
+
+    public static void main(String[] args) {
+
+        TreeMap<Integer, Integer> myMap = new TreeMap<Integer, Integer>();
+        if(myMap.containsKey(42))
+            System.out.println("Element 42 is in the map");
+        else
+            System.out.println("Can not find element 42");
+
+        System.out.println(myMap.get(42)); // 输出 null
+
+        // Java不存在C++中默认的访问key即添加默认(key, value)的行为
+        // 以下代码仍然无法找到42
+        if(myMap.containsKey(42))
+            System.out.println("Element 42 is in the map");
+        else
+            System.out.println("Can not find element 42");
+
+        myMap.put(42, 0);
+        myMap.put(42, myMap.get(42) + 1);
+        System.out.println(myMap.get(42)); // 输出 1
+        if(myMap.containsKey(42))
+            System.out.println("Element 42 is in the map");
+        else
+            System.out.println("Can not find element 42");
+
+        myMap.put(42, myMap.get(42) - 1);
+        System.out.println(myMap.get(42)); // 输出 0
+
+        // 注意: key对应的值为0, 不代表key不存在
+        if(myMap.containsKey(42))
+            System.out.println("Element 42 is in the map");
+        else
+            System.out.println("Can not find element 42");
+
+        // 注意： 也不可以为key对应的值设置null来删除一个key
+        myMap.put(42, null);
+        if(myMap.containsKey(42))
+            System.out.println("Element 42 is in the map");
+        else
+            System.out.println("Can not find element 42");
+
+        // 使用remove删除一个key
+        myMap.remove(42);
+        if(myMap.containsKey(42))
+            System.out.println("Element 42 is in the map");
+        else
+            System.out.println("Can not find element 42");
+    }
+}
diff --git a/04-Using-Hash-Table/Course Code (Java)/02-Intersection-of-Two-Arrays-II/src/Solution.java b/04-Using-Hash-Table/Course Code (Java)/02-Intersection-of-Two-Arrays-II/src/Solution.java
@@ -0,0 +1,44 @@
+import java.util.TreeMap;
+import java.util.ArrayList;
+
+/// 350. Intersection of Two Arrays II
+public class Solution {
+
+    public int[] intersect(int[] nums1, int[] nums2) {
+
+        TreeMap<Integer, Integer> record = new TreeMap<Integer, Integer>();
+        for(int num: nums1)
+            if(!record.containsKey(num))
+                record.put(num, 1);
+            else
+                record.put(num, record.get(num) + 1);
+
+        ArrayList<Integer> result = new ArrayList<Integer>();
+        for(int num: nums2)
+            if(record.containsKey(num) && record.get(num) > 0){
+                result.add(num);
+                record.put(num, record.get(num) - 1);
+            }
+
+        int[] ret = new int[result.size()];
+        int index = 0;
+        for(Integer num: result)
+            ret[index++] = num;
+
+        return ret;
+    }
+
+    private static void printArr(int[] arr){
+        for(int e: arr)
+            System.out.print(e + " ");
+        System.out.println();
+    }
+
+    public static void main(String[] args) {
+
+        int[] nums1 = {1, 2, 2, 1};
+        int[] nums2 = {2, 2};
+        int[] res = (new Solution()).intersect(nums1, nums2);
+        printArr(res);
+    }
+}
