LeetCode:926. 将字符串翻转到单调递增

 

暴力法超时：思想：动态规划

public int minFlipsMonoIncrb(String S) {
        int result = S.length();
        for (int i = 0; i < S.length(); i++) {
            char[] str1 = S.substring(0, i).toCharArray();
            char[] str2 = S.substring(i + 1, S.length()).toCharArray();
            int zero = 0;
            int one = 0;
            for (int j = 0; j < str1.length; j++) {
                if (str1[j] == '1')
                    zero++;
            }
            for (int j = 0; j < str2.length; j++) {
                if (str2[j] == '0')
                    one++;
            }
            int re = zero + one;
            if (re < result)
                result = re;
        }
        return result;
    }

优化后：

public int minFlipsMonoIncr(String S) {
        int result = S.length();
        int zero = 0;
        int leftOne = 0;
        int rightZero = 0;
        for (int i = 0; i < S.length(); i++) {
            if (S.charAt(i) == '0')
                zero++;
        }
        rightZero = zero;
        for (int i = -1; i < S.length(); i++) {
            if (i == -1) {

            } else {
                if (S.charAt(i) == '0') {
                    rightZero--;
                }
                if (S.charAt(i) == '1') {
                    leftOne++;
                }
            }
            int re = leftOne + rightZero;
            if (re < result)
                result = re;
        }
        return result;
    }