Formatted question description: https://leetcode.ca/all/2027.html

2027. Minimum Moves to Convert String (Easy)

You are given a string s consisting of n characters which are either 'X' or 'O'.

A move is defined as selecting three consecutive characters of s and converting them to 'O'. Note that if a move is applied to the character 'O', it will stay the same.

Return the minimum number of moves required so that all the characters of s are converted to 'O'.

 

Example 1:

Input: s = "XXX"
Output: 1
Explanation: XXX -> OOO
We select all the 3 characters and convert them in one move.

Example 2:

Input: s = "XXOX"
Output: 2
Explanation: XXOX -> OOOX -> OOOO
We select the first 3 characters in the first move, and convert them to 'O'.
Then we select the last 3 characters and convert them so that the final string contains all 'O's.

Example 3:

Input: s = "OOOO"
Output: 0
Explanation: There are no 'X's in s to convert.

 

Constraints:

  • 3 <= s.length <= 1000
  • s[i] is either 'X' or 'O'.

Solution 1.

// OJ: https://leetcode.com/problems/minimum-moves-to-convert-string/
// Time: O(N)
// Space: O(1)
class Solution {
public:
    int minimumMoves(string s) {
        int N = s.size(), ans = 0;
        for (int i = 0; i < N;) {
            if (s[i] == 'O') ++i;
            else ++ans, i += 3;
        }
        return ans;
    }
};

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