[leetcode-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]

思路：

暴力枚举所有交换可能，竟然没有超时。。。感觉因为输入最多到10⁸

最多8位，复杂度O(n³)虽然很高，但数据规模小，但总之不是什么好办法。

vector<int> digits(int num)
{
    if (num == 0)return{0};
    vector<int> ret;    
    while (num > 0)
    {
        ret.push_back(num % 10);
        num /= 10;
    }
    reverse(ret.begin(), ret.end());
    return ret;
}
int toNum(vector<int>num)
{
    int r = 0;
    for (int i = 0; i < num.size();i++)
    {
        r *= 10;
        r += num[i];
    }
    return r;
}
int maximumSwap(int n)
{
    vector<int> num = digits(n);
    int m = n;

    for (int i = 0; i < num.size();i++)
    {
        for (int j = i + 1; j < num.size();j++)
        {
            swap(num[i], num[j]);
            m = max(m, toNum(num));
            swap(num[i], num[j]);
        }
    }
    return m;
}