1758. Minimum Changes To Make Alternating Binary String

Description

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 <= 104
  • s[i] is either '0' or '1'.

Solutions

Solution 1

Python Code
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class Solution:
    def minOperations(self, s: str) -> int:
        cnt = sum(c != '01'[i & 1] for i, c in enumerate(s))
        return min(cnt, len(s) - cnt)

Java Code
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class Solution {
    public int minOperations(String s) {
        int cnt = 0, n = s.length();
        for (int i = 0; i < n; ++i) {
            cnt += (s.charAt(i) != "01".charAt(i & 1) ? 1 : 0);
        }
        return Math.min(cnt, n - cnt);
    }
}

C++ Code
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class Solution {
public:
    int minOperations(string s) {
        int cnt = 0, n = s.size();
        for (int i = 0; i < n; ++i) cnt += s[i] != "01"[i & 1];
        return min(cnt, n - cnt);
    }
};

Go Code
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func minOperations(s string) int {
	cnt := 0
	for i, c := range s {
		if c != []rune("01")[i&1] {
			cnt++
		}
	}
	return min(cnt, len(s)-cnt)
}

TypeScript Code
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function minOperations(s: string): number {
    const n = s.length;
    let count = 0;
    for (let i = 0; i < n; i++) {
        count += s[i] !== '01'[i & 1] ? 1 : 0;
    }
    return Math.min(count, n - count);
}

Rust Code
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impl Solution {
    pub fn min_operations(s: String) -> i32 {
        let n = s.len();
        let s = s.as_bytes();
        let cs = [b'0', b'1'];
        let mut count = 0;
        for i in 0..n {
            count += if s[i] != cs[i & 1] { 1 } else { 0 };
        }
        count.min(n - count) as i32
    }
}

C Code
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#define min(a, b) (((a) < (b)) ? (a) : (b))

int minOperations(char* s) {
    int n = strlen(s);
    int count = 0;
    for (int i = 0; i < n; i++) {
        count += s[i] != ('0' + (i & 1)) ? 0 : 1;
    }
    return min(count, n - count);
}