LeetCode 670: Maximum Swap

Note:

1. Scan from the small level.

2. Only take the index larger one if same digits. 

 

class Solution {
    public int maximumSwap(int num) {
        if (num < 12) {
            return num;
        }
        
        List<Integer> digits = new ArrayList<>();
        while (num > 0) {
            digits.add(0, num % 10);
            num /= 10;
        }
        
        int[] rightMax = new int[digits.size()];
        rightMax[digits.size() - 1] = digits.size() - 1;
        for (int i = digits.size() - 2; i >= 0; i--) {
            rightMax[i] = digits.get(rightMax[i + 1]) < digits.get(i + 1) ? i + 1 : rightMax[i + 1];
        }
        
        int result = 0;
        boolean found = false;
        for (int i = 0; i < digits.size(); i++) {
            if (!found && i < rightMax[i] && digits.get(i) < digits.get(rightMax[i])) {
                result = result * 10 + digits.get(rightMax[i]);
                digits.set(rightMax[i], digits.get(i));
                found = true;
            } else {
                result = result * 10 + digits.get(i);
            }
        }
        return result;
    }
}