0670-Medium-Maximum-Swap.java

class Solution {
    public int maximumSwap(int num) {
      char[] digits = String.valueOf(num).toCharArray();

      int[] lastOccurrence = new int[10];

      for (int i = 0; i < digits.length; i++)
        lastOccurrence[digits[i] - '0'] = i;

      for (int i = 0; i < digits.length; i++) {
        for (int d = 9; d > digits[i] - '0'; d--) {
          if (lastOccurrence[d] > i) {
            char temp = digits[i];
            digits[i] = digits[lastOccurrence[d]];
            digits[lastOccurrence[d]] = temp;

            return Integer.parseInt(new String(digits));
          }
        }
      }

      return num;
    }
}