926. Flip String to Monotone Increasing

Problem

A binary string is monotone increasing if it consists of some number of 0's (possibly none), followed by some number of 1's (also possibly none).

You are given a binary string s. You can flip s[i] changing it from 0 to 1 or from 1 to 0.

Return **the minimum number of flips to make *s* monotone increasing**.

  Example 1:

Input: s = "00110"
Output: 1
Explanation: We flip the last digit to get 00111.

Example 2:

Input: s = "010110"
Output: 2
Explanation: We flip to get 011111, or alternatively 000111.

Example 3:

Input: s = "00011000"
Output: 2
Explanation: We flip to get 00000000.

  Constraints:

• 1 <= s.length <= 10^5

• s[i] is either '0' or '1'.

Solution (Java)

class Solution {
    public int minFlipsMonoIncr(String s) {
        if (s == null || s.length() <= 1) {
            return 0;
        }
        final int n = s.length();
        int countOnes = 0;
        int countFlips = 0;
        for (int i = 0; i < n; i++) {
            if (s.charAt(i) == '0') {
                if (countOnes == 0) {
                    continue;
                } else {
                    countFlips++;
                }
            } else {
                countOnes++;
            }
            countFlips = Math.min(countFlips, countOnes);
        }
        return countFlips;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).