670. Maximum Swap

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原文链接：http://www.cnblogs.com/ruruozhenhao/p/10655283.html

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#java

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:

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;
    }
}