670

670. Maximum Swap (Medium)

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]

Solution 1.

// OJ: https://leetcode.com/problems/maximum-swap/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1)
class Solution {
public:
    int maximumSwap(int num) {
        string digits = to_string(num), memo(digits.size(), '\0');
        int maxIndex = digits.size() - 1;
        for (int i = digits.size() - 1; i >= 0; --i) {
            if (digits[i] > digits[maxIndex]) maxIndex = i;
            memo[i] = maxIndex;
        }
        for (int i = 0; i < digits.size(); ++i) {
            if (memo[i] > i && digits[i] != digits[memo[i]]) {
                swap(digits[i], digits[memo[i]]);
                return stoi(digits);
            }
        }
        return num;
    }
};

Solution 2.

// OJ: https://leetcode.com/problems/maximum-swap/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1)
class Solution {
public:
    int maximumSwap(int num) {
        string digits = to_string(num);
        int last[10] = {};
        for (int i = 0; i < digits.size(); ++i) last[digits[i] - '0'] = i;
        for (int i = 0; i < digits.size(); ++i) {
            for (int j = 9; j > digits[i] - '0'; --j) {
                if (last[j] > i) {
                    swap(digits[i], digits[last[j]]);
                    return stoi(digits);
                }
            }
        }
        return num;
    }
};