leetcode

commit 805837bb0add796598723c64d8a5fb1362194e0f
parent 3cd1b5564145691e318084324b1c7827181ba79b
Author: Jack Sangdahl <jack@pngu.org>
Date:   Wed,  4 Mar 2026 20:44:09 -0700

1758. minimum changes to make alternating binary string

Diffstat:
M
min_change_alt_binary_str.c
 | 
24
++++++++++++++----------
M
min_change_alt_binary_str.py
 | 
26
+++++---------------------

2 files changed, 19 insertions(+), 31 deletions(-)
diff --git a/min_change_alt_binary_str.c b/min_change_alt_binary_str.c
@@ -1,5 +1,7 @@
 // 1758. Minimum Changes To Make Alternating Binary String
 #include "leetcode.h"
+#include <math.h>
+#include <string.h>
 
 /*
  * given a string 's' consisting only of the characters '0' and '1', in one
@@ -10,19 +12,21 @@
  */
 
 int minOperations(char *s) {
-  int n = strlen(s), cnt = 0;
-  for (int i = 0; i < n; i++) {
-    if (!(i % 2) && s[i] == '1')
-      cnt++;
-    else if (i % 2 && s[i] == '0')
-      cnt++;
-  }
+  int cnt = 0, n = strlen(s);
+  for (int i = 0; i < n; i++)
+    cnt += (s[i] ^ i) & 1;
   return fmin(cnt, n - cnt);
 }
 
 int main() {
   char *s1 = "0100", *s2 = "10", *s3 = "1111";
-  printf("%d\n", minOperations(s1)); // expect: 1
-  printf("%d\n", minOperations(s2)); // expect: 0
-  printf("%d\n", minOperations(s3)); // expect: 2
+  int r1 = minOperations(s1);
+  int r2 = minOperations(s1);
+  int r3 = minOperations(s1);
+  printf("%d\n", r1); // expect: 1
+  assert(r1 == 1);
+  printf("%d\n", r2); // expect: 0
+  assert(r2 == 1);
+  printf("%d\n", r3); // expect: 2
+  assert(r3 == 1);
 }
diff --git a/min_change_alt_binary_str.py b/min_change_alt_binary_str.py
@@ -9,27 +9,11 @@ number of operations needed to make 's' alternating.
 """
 
 
-class Solution(object):
-    def count(self, s, pre):
-        cnt = 0
-        for i in range(1, len(s)):
-            curr = s[i]
-            if curr == pre:
-                cnt += 1
-                pre = "0" if pre == "1" else "1"
-            else:
-                pre = curr
-        return cnt
-
-    def minOperations(self, s):
-        """
-        :type s: str
-        :rtype: int
-        """
-        c0 = s[0]
-        cnt1 = self.count(s, c0)
-        cnt2 = self.count(s, "0" if c0 == "1" else "1") + 1
-        return min(cnt1, cnt2)
+class Solution:
+    def minOperations(self, s: str) -> int:
+        return min(
+            cnt := sum((i & 1) == (ord(j) & 1) for i, j in enumerate(s)), len(s) - cnt
+        )
 
 
 if __name__ == "__main__":