solutions: 1758 - Minimum Changes To Make Alternating Binary String (…

…Easy)

solutions/1700-1799/1758-minimum-changes-to-make-alternating-binary-string-easy.md

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+---
+description: 'Author: @jit, @wingkwong | https://leetcode.com/problems/minimum-changes-to-make-alternating-binary-string/'
+tags: [String]
+---
+
+# 1758 - Minimum Changes To Make Alternating Binary String (Easy)
+
+## Problem Link
+
+https://leetcode.com/problems/minimum-changes-to-make-alternating-binary-string/
+
+## Problem Statement
+
+You are given a string `s` consisting only of the characters `'0'` and `'1'`. In one operation, you can change any `'0'` to `'1'` or vice versa.
+
+The string is called alternating if no two adjacent characters are equal. For example, the string `"010"` is alternating, while the string `"0100"` is not.
+
+Return *the **minimum** number of operations needed to make* `s` *alternating*.
+
+**Example 1:**
+
+```
+Input: s = "0100"
+Output: 1
+Explanation: If you change the last character to '1', s will be "0101", which is alternating.
+```
+
+**Example 2:**
+
+```
+Input: s = "10"
+Output: 0
+Explanation: s is already alternating.
+```
+
+**Example 3:**
+
+```
+Input: s = "1111"
+Output: 2
+Explanation: You need two operations to reach "0101" or "1010".
+```
+
+**Constraints:**
+
+- $1 <= s.length <= 10^4$
+- `s[i]` is either `'0'` or `'1'`.
+
+## Approach 1: Counting
+
+<Tabs>
+<TabItem value="scala" label="Scala">
+<SolutionAuthor name="@jit"/>
+
+```scala
+object Solution {
+  // Count swaps required for an alternating string starting with 0.
+  // The alternating string starting with 1 is just the complement.
+  def minOperations(s: String): Int = {
+    val zSwaps = s.indices.count(i => s(i).asDigit == i % 2)
+    zSwaps min (s.length - zSwaps)
+  }
+}
+```
+
+</TabItem>
+
+<TabItem value="cpp" label="C++">
+<SolutionAuthor name="@wingkwong"/>
+
+```cpp
+class Solution {
+public:
+    int minOperations(string s) {
+        int cnt = 0, n = s.size();
+        for (int i = 0; i < n; i++) cnt += s[i] - '0' == i % 2;
+        return min(cnt, n - cnt);
+    }
+};
+```
+
+</TabItem>
+</Tabs>