670. Maximum Swap

Given a non-negative integer, you could swap two digits at most once to get the maximum valued number. Return the maximum valued number you could get.

Example 1:

Input: 2736
Output: 7236
Explanation: Swap the number 2 and the number 7.

Example 2:

Input: 9973
Output: 9973
Explanation: No swap.

Note:

1. The given number is in the range [0, 108]

Approach #1: Math. [Java]

class Solution {
    public int maximumSwap(int num) {
        char[] digits = Integer.toString(num).toCharArray();
        int[] buckets = new int[10];
        for (int i = 0; i < digits.length; ++i)
            buckets[digits[i]-'0'] = i;

        for (int i = 0; i < digits.length; ++i) {
            for (int j = 9; j > digits[i]-'0'; --j) {
                if (buckets[j] > i) {
                    char temp = digits[i];
                    digits[i] = digits[buckets[j]];
                    digits[buckets[j]] = temp;
                    return Integer.valueOf(new String(digits));
                }
            }
        }

        return num;
    }
}

　　

Analysis:

https://leetcode.com/problems/maximum-swap/discuss/107068/Java-simple-solution-O(n)-time