README_EN.md

1202. Smallest String With Swaps

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Description

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.

Return the lexicographically smallest string that s can be changed to after using the swaps.

 

Example 1:

Input: s = "dcab", pairs = [[0,3],[1,2]]
Output: "bacd"
Explaination: 
Swap s[0] and s[3], s = "bcad"
Swap s[1] and s[2], s = "bacd"

Example 2:

Input: s = "dcab", pairs = [[0,3],[1,2],[0,2]]
Output: "abcd"
Explaination: 
Swap s[0] and s[3], s = "bcad"
Swap s[0] and s[2], s = "acbd"
Swap s[1] and s[2], s = "abcd"

Example 3:

Input: s = "cba", pairs = [[0,1],[1,2]]
Output: "abc"
Explaination: 
Swap s[0] and s[1], s = "bca"
Swap s[1] and s[2], s = "bac"
Swap s[0] and s[1], s = "abc"

 

Constraints:

• 1 <= s.length <= 10^5
• 0 <= pairs.length <= 10^5
• 0 <= pairs[i][0], pairs[i][1] < s.length
• s only contains lower case English letters.

Solutions

Python3

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))

Java

class Solution {
    private int[] p;

    public String smallestStringWithSwaps(String s, List<List<Integer>> pairs) {
        int n = s.length();
        p = new int[n];
        List<Character>[] d = new List[n];
        for (int i = 0; i < n; ++i) {
            p[i] = i;
            d[i] = new ArrayList<>();
        }
        for (var pair : pairs) {
            int a = pair.get(0), b = pair.get(1);
            p[find(a)] = find(b);
        }
        char[] cs = s.toCharArray();
        for (int i = 0; i < n; ++i) {
            d[find(i)].add(cs[i]);
        }
        for (var e : d) {
            e.sort((a, b) -> b - a);
        }
        for (int i = 0; i < n; ++i) {
            var e = d[find(i)];
            cs[i] = e.remove(e.size() - 1);
        }
        return String.valueOf(cs);
    }

    private int find(int x) {
        if (p[x] != x) {
            p[x] = find(p[x]);
        }
        return p[x];
    }
}

C++

class Solution {
public:
    string smallestStringWithSwaps(string s, vector<vector<int>>& pairs) {
        int n = s.size();
        int p[n];
        iota(p, p + n, 0);
        vector<char> d[n];
        function<int(int)> find = [&](int x) -> int {
            if (p[x] != x) {
                p[x] = find(p[x]);
            }
            return p[x];
        };
        for (auto e : pairs) {
            int a = e[0], b = e[1];
            p[find(a)] = find(b);
        }
        for (int i = 0; i < n; ++i) {
            d[find(i)].push_back(s[i]);
        }
        for (auto& e : d) {
            sort(e.rbegin(), e.rend());
        }
        for (int i = 0; i < n; ++i) {
            auto& e = d[find(i)];
            s[i] = e.back();
            e.pop_back();
        }
        return s;
    }
};

Go

func smallestStringWithSwaps(s string, pairs [][]int) string {
	n := len(s)
	p := make([]int, n)
	d := make([][]byte, n)
	for i := range p {
		p[i] = i
	}
	var find func(int) int
	find = func(x int) int {
		if p[x] != x {
			p[x] = find(p[x])
		}
		return p[x]
	}
	for _, pair := range pairs {
		a, b := pair[0], pair[1]
		p[find(a)] = find(b)
	}
	cs := []byte(s)
	for i, c := range cs {
		j := find(i)
		d[j] = append(d[j], c)
	}
	for i := range d {
		sort.Slice(d[i], func(a, b int) bool { return d[i][a] > d[i][b] })
	}
	for i := range cs {
		j := find(i)
		cs[i] = d[j][len(d[j])-1]
		d[j] = d[j][:len(d[j])-1]
	}
	return string(cs)
}

TypeScript

function smallestStringWithSwaps(s: string, pairs: number[][]): string {
    const n = s.length;
    const p = new Array(n).fill(0).map((_, i) => i);
    const find = (x: number): number => {
        if (p[x] !== x) {
            p[x] = find(p[x]);
        }
        return p[x];
    };
    const d: string[][] = new Array(n).fill(0).map(() => []);
    for (const [a, b] of pairs) {
        p[find(a)] = find(b);
    }
    for (let i = 0; i < n; ++i) {
        d[find(i)].push(s[i]);
    }
    for (const e of d) {
        e.sort((a, b) => b.charCodeAt(0) - a.charCodeAt(0));
    }
    const ans: string[] = [];
    for (let i = 0; i < n; ++i) {
        ans.push(d[find(i)].pop()!);
    }
    return ans.join('');
}

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