solution of 1888 in java

java/1888. Minimum Number of Flips to Make the Binary String Alternating.java

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+class Solution {
+    public int minFlips(String s) {
+        int n = s.length();
+        String doubled = s + s;
+
+        // Build alternating patterns of length 2n
+        StringBuilder alt1 = new StringBuilder(); // 010101...
+        StringBuilder alt2 = new StringBuilder(); // 101010...
+
+        for (int i = 0; i < 2 * n; i++) {
+            alt1.append(i % 2 == 0 ? '0' : '1');
+            alt2.append(i % 2 == 0 ? '1' : '0');
+        }
+
+        int res = Integer.MAX_VALUE;
+        int diff1 = 0, diff2 = 0;
+        int left = 0;
+
+        for (int right = 0; right < 2 * n; right++) {
+
+            if (doubled.charAt(right) != alt1.charAt(right)) diff1++;
+            if (doubled.charAt(right) != alt2.charAt(right)) diff2++;
+
+            // Keep window size = n
+            if (right - left + 1 > n) {
+                if (doubled.charAt(left) != alt1.charAt(left)) diff1--;
+                if (doubled.charAt(left) != alt2.charAt(left)) diff2--;
+                left++;
+            }
+
+            // When window size is n, update result
+            if (right - left + 1 == n) {
+                res = Math.min(res, Math.min(diff1, diff2));
+            }
+        }
+
+        return res;
+    }
+}