Smallest String With Swaps — LeetCode 1202 Python Solution

The problem

You are given a string s, and an array of pairs of indices in the string pairs where pairs[i] = [a, b] indicates 2 indices(0-indexed) of the string. You can swap the characters at any pair of indices in the given pairs any number of times.

Example

Input

s = "dcab", pairs = [[0,3],[1,2]]

Output

"bacd"

Python solution

class Solution:
    def smallestStringWithSwaps(self, s: str, pairs: List[List[int]]) -> str:
        def find(x: int) -> int:
            if p[x] != x:
                p[x] = find(p[x])
            return p[x]

        n = len(s)
        p = list(range(n))
        for a, b in pairs:
            p[find(a)] = find(b)
        d = defaultdict(list)
        for i, c in enumerate(s):
            d[find(i)].append(c)
        for i in d.keys():
            d[i].sort(reverse=True)
        return "".join(d[find(i)].pop() for i in range(n))

Complexity

Pattern: Union-Find

Merge groups and ask whether two things are connected, both in near-constant time. LeetCode 1202. Smallest String With Swaps is filed here because LeetCode tags it Union Find, which is the vocabulary this hub collects.

The union-find guide has the Python template for the pattern and the 83 LeetCode problems that use it.

Related problems