Add Longest Uniform Substring After Replacements

Author: marttp

kotlin/Sliding Windows/LongestUniformSubstringAfterReplacements.kt

@@ -0,0 +1,30 @@
+fun longestUniformSubstringAfterReplacements(s: String, k: Int): Int {
+    val freqs = mutableMapOf<Char, Int>()
+    var highestFreq = 0
+    var maxLen = 0
+    var left = 0
+    var right = 0
+    while (right < s.length) {
+        // Update the frequency of the character at the right pointer
+        // and the highest frequency for the current window.
+        freqs[s[right]] = freqs.getOrDefault(s[right], 0) + 1
+        highestFreq = maxOf(highestFreq, freqs[s[right]]!!)
+        // Calculate replacements needed for the current window.
+        val numCharsToReplace = (right - left + 1) - highestFreq
+        // Slide the window if the number of replacements needed exceeds
+        // 'k'. The right pointer always gets advanced, so we just need
+        // to advance 'left'.
+        if (numCharsToReplace > k) {
+            // Remove the character at the left pointer from the hash map
+            // before advancing the left pointer.
+            freqs[s[left]] = freqs[s[left]]!! - 1
+            left++
+        }
+        // Since the length of the current window increases or stays the
+        // same, assign  the length of the current window to 'maxLen'.
+        maxLen = right - left + 1
+        // Expand the window.
+        right++
+    }
+    return maxLen
+}