Create 1888-minimum-number-of-flips-to-make-the-binary-string-alternating.kt

Author: a93a

kotlin/1888-minimum-number-of-flips-to-make-the-binary-string-alternating.kt

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+/*
+* O(N) memory
+*/
+    fun minFlips(s: String): Int {
+        var s2 = s + s
+        var sb1 = StringBuilder()
+        var sb2 = StringBuilder()
+        
+        for (i in 0 until s2.length) {
+            if (i % 2 == 0) {
+                sb1.append('1')
+                sb2.append('0')
+            } else {
+                sb1.append('0')
+                sb2.append('1')
+            }
+        }
+
+        val alt1 = sb1.toString()
+        val alt2 = sb2.toString()
+        var res = s2.length
+        var diff1 = 0
+        var diff2 = 0
+        var left = 0
+        
+        for (right in 0 until s2.length) {
+            if (s2[right] != alt1[right])
+                diff1++
+            if (s2[right] != alt2[right])
+                diff2++
+            if (right - left + 1 > s.length) {
+                if (s2[left] != alt1[left])
+                    diff1--
+                if (s2[left] != alt2[left])
+                    diff2--
+                left++
+            }
+
+            if (right - left + 1 == s.length)
+                res = minOf(res, diff1, diff2)
+        }
+
+        return res
+    }
+}
+
+/*
+* O(1) memory
+*/
+class Solution {
+    fun minFlips(s: String): Int {
+        val n = s.length
+        var diff1 = 0
+        var diff2 = 0
+        var res = n
+
+        for (i in 0 until n * 2) {
+            val sChar = s[i % n]
+            val is0 = if (i % 2 == 0) '0' else '1'
+            if (sChar != is0)
+                diff1++
+            else
+                diff2++
+            
+            if (i >= n) {
+                val firstCharInWindow = if ((i - n) % 2 == 0) '0' else '1'
+                if (firstCharInWindow != s[i - n])
+                    diff1--
+                else
+                    diff2--
+
+                res = minOf(res, diff1, diff2)
+            }
+        }
+
+        return res
+    }
+}