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926. Flip String to Monotone Increasing

Explanation:

To solve this problem, we can use a dynamic programming approach. We need to find the minimum number of flips to make the string monotone increasing. We can iterate through the string and keep track of two values: the number of ones before the current position and the number of flips needed to make the string monotone increasing up to that position.

At each position, we have two choices:

  1. If the current character is '0', we can either keep it as '0' and add a flip, or we can change it to '1' without any flip. We choose the minimum of these two options.
  2. If the current character is '1', we just need to update the count of ones before the current position.

Finally, the minimum number of flips to make the entire string monotone increasing is the minimum of flips needed at the last position (when the string ends with '0') and the number of ones in the string.

  • Time complexity: O(n), where n is the length of the input string s.
  • Space complexity: O(1).

:

class Solution {
    public int minFlipsMonoIncr(String s) {
        int onesBefore = 0;
        int flips = 0;
        
        for (char c : s.toCharArray()) {
            if (c == '0') {
                flips = Math.min(flips + 1, onesBefore);
            } else {
                onesBefore++;
            }
        }
        
        return flips;
    }
}

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