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]

只交换一次整数中的两个数，获得最大的值

思路：从高位向低扫描，如果后面某位的数大于等于当前位的值，交换位置后即得到最大值。

 

    public int maximumSwap(int num) {
//        从高位向低扫描，如果后面某位的数大于等于当前位的值，交换位置后即得到最大值
        char[] dig = String.valueOf(num).toCharArray();
        int maxIndex = 0;
        while (maxIndex < dig.length - 1) {
            int newMaxIndex = maxIndex;
            for (int i = maxIndex + 1; i < dig.length; i++) {
                if (dig[newMaxIndex] <= dig[i])  newMaxIndex = i;
            }
            if (newMaxIndex != maxIndex && dig[newMaxIndex] != dig[maxIndex]) {
                char temp = dig[newMaxIndex];
                dig[newMaxIndex] = dig[maxIndex];
                dig[maxIndex] = temp;
                return Integer.valueOf(new String(dig));
            }else  maxIndex++;//当前maxIndex的后面没有大于等于它的数字了
        }
        return num;
    }