MinimumChangesToMakeAlternatingBinaryString.cpp

// Source : https://leetcode.com/problems/minimum-changes-to-make-alternating-binary-string/
// Author : Hao Chen
// Date   : 2021-02-14

/***************************************************************************************************** 
 *
 * 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'.
 ******************************************************************************************************/

class Solution {
public:
    int minOperations(string s) {
        int start_with_zero = 0;
        int start_with_one = 0;
        for (int i=0; i<s.size(); i++){
            if (i % 2 == 0) {
                s[i] == '1' ? start_with_zero++ : start_with_one++;
            }else{
                s[i] == '0' ? start_with_zero++ : start_with_one++;
            }
        }
        return std::min(start_with_zero, start_with_one);
    }
};