LeetCode-Maximum Swap

2019年11月6日 132次阅读

1. Maximum Swap （Medium）

Description
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, 10^8]

Analysis
因为题目的最大数字只有八位，所以直接暴力枚举出所有交换一次后得到的数字也不会超时，时间复杂度为O(n^3)。

代码：

class Solution {
public:
    int toNum(const vector<int> &num) {
        int r = 0;
        for (int i : num) {
            r *= 10;
            r += i;
        }
        return r;
    }

    int maximumSwap(int num) {
        vector<int> digits;
        int temp = num;
        do {
            digits.push_back(temp % 10);
        } while ((temp /= 10) != 0);
        reverse(digits.begin(), digits.end());
        int m = num;

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