subject

answer

Time complexity O(n)

Ideas

Greedy Algorithm , hypothesis G On the left B On the right , The first one. G Put it in the first place , How many steps does it take , Put the second G Put it in the second position , How many steps does it take , And so on .

Code

public class Solution {
    
    public static int minSteps(String s) {
    
        if (null == s || s.length() == 0) {
    
            return 0;
        }

        char[] chars = s.toCharArray();
        int gLast = 0;
        int gRes = 0;
        for (int i = 0; i < chars.length; i++) {
    
            if (chars[i] == 'G') {
    
                gRes += i - gLast;
                gLast++;
            }
        }

        int bLast = 0;
        int bRes = 0;
        for (int i = 0; i < chars.length; i++) {
    
            if (chars[i] == 'B') {
    
                bRes += i - bLast;
                bLast++;
            }
        }

        return Math.min(gRes, bRes);
    }
}