44 lines
1.5 KiB
C++
44 lines
1.5 KiB
C++
#include <vector>
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#include <unordered_set>
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#include <algorithm>
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#include <functional>
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#include <iostream>
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/**
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* 1466. Reorder Routes to Make All Paths Lead to the City Zero
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*
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* There are n cities numbered from 0 to n - 1 and n - 1 roads such that there is only one way to travel between two different cities (this network form a tree). Last year, The ministry of transport decided to orient the roads in one direction because they are too narrow.
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* Roads are represented by connections where connections[i] = [ai, bi] represents a road from city ai to city bi.
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* This year, there will be a big event in the capital (city 0), and many people want to travel to this city.
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* Your task consists of reorienting some roads such that each city can visit the city 0. Return the minimum number of edges changed.
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* It's guaranteed that each city can reach city 0 after reorder.
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*/
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class Solution {
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public:
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static int minReorder(int n, const std::vector<std::vector<int>>& connections) {
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std::vector<std::unordered_set<int>> vs(n);
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for (const auto& i : connections) {
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vs[i[0]].insert(-i[1]);
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vs[i[1]].insert(i[0]);
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}
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std::vector<bool> vis(n);
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std::function<int(int)> dfs = [&](int cur) {
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vis[cur] = true;
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int ret = 0;
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for (int nx : vs[cur])
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if (!vis[std::abs(nx)])
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ret += (nx < 0) + dfs(std::abs(nx));
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return ret;
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};
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return dfs(0);
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}
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};
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int main() {
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std::cout << Solution::minReorder(6, {
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{0, 1}, {1, 3}, {2, 3}, {4, 0}, {4, 5}
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});
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return 0;
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}
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