Maximum Swap — LeetCode 670 Python Solution

The problem

You are given an integer num. You can swap two digits at most once to get the maximum valued number.

Example

Input

num = 2736

Output

7236

Explanation

Swap the number 2 and the number 7.

Python solution

class Solution:
    def maximumSwap(self, num: int) -> int:
        s = list(str(num))
        n = len(s)
        d = list(range(n))
        for i in range(n - 2, -1, -1):
            if s[i] <= s[d[i + 1]]:
                d[i] = d[i + 1]
        for i, j in enumerate(d):
            if s[i] < s[j]:
                s[i], s[j] = s[j], s[i]
                break
        return int(''.join(s))

Complexity

Pattern: Greedy

Take the locally best option every time — when you can prove that never costs you later. LeetCode 670. Maximum Swap is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Greedy.

The greedy guide has the Python template for the pattern and the 346 LeetCode problems that use it.

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