53 lines
1.2 KiB
C++
53 lines
1.2 KiB
C++
#include <vector>
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#include <numeric>
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#include <unordered_map>
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#include <iostream>
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class UnionFindSet {
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private:
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std::vector<int> f;
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public:
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explicit UnionFindSet(int n) : f(n + 1) {
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std::iota(f.begin(), f.end(), 0);
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}
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int find(int x) {
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return (x == f[x]) ? x : (f[x] = find(f[x]));
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}
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// Merge y to x
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int uni(int x, int y) {
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return f[find(y)] = find(x);
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}
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};
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/**
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* 2316. Count Unreachable Pairs of Nodes in an Undirected Graph
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*
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* You are given an integer n. There is an undirected graph with n nodes, numbered from 0 to n - 1. You are given a 2D integer array edges where edges[i] = [ai, bi] denotes that there exists an undirected edge connecting nodes ai and bi.
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* Return the number of pairs of different nodes that are unreachable from each other.
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*/
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class Solution {
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public:
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static long long countPairs(int n, const std::vector<std::vector<int>>& edges) {
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UnionFindSet ufs(n);
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for (auto&& i : edges)
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ufs.uni(i[0], i[1]);
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std::unordered_map<int, int> m;
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for (int i = 0; i < n; ++i)
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++m[ufs.find(i)];
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long long ret = 0;
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for (auto&& [_, cnt] : m)
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ret += (long long)(n - cnt) * (long long)(cnt);
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return ret >> 1;
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}
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};
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int main() {
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std::cout << Solution::countPairs(7, {
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{0,2},{0,5},{2,4},{1,6},{5,4}
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});
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}
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