77 lines
1.6 KiB
C++
77 lines
1.6 KiB
C++
#include <vector>
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#include <queue>
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#include <cstring>
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class Solution {
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public:
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static std::vector<int> findMinHeightTrees(int n, const std::vector<std::vector<int>>& edges) {
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if (n == 1)
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return {0};
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int degrees[n], ans[n];
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std::vector<int> G[n];
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std::memset(degrees, 0, sizeof degrees);
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std::memset(ans, 0, sizeof ans);
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for (const auto& e : edges) {
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G[e[0]].push_back(e[1]);
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G[e[1]].push_back(e[0]);
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++degrees[e[0]];
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++degrees[e[1]];
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}
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int x, y, distXY;
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int father[n];
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{
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int dist[n];
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bool vis[n];
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std::queue<int> q;
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auto doBFS = [&](int startNode) {
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q.push(startNode);
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q.push(0);
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std::memset(vis, 0, sizeof vis);
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std::memset(father, 0, sizeof father);
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vis[startNode] = true;
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while (!q.empty()) {
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int idx = q.front();
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q.pop();
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int len = q.front();
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q.pop();
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dist[idx] = len;
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for (int nextId : G[idx]) {
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if (vis[nextId])
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continue;
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vis[nextId] = true;
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father[nextId] = idx;
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q.push(nextId);
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q.push(len + 1);
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}
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}
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};
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// From 0, find the max distance
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doBFS(0);
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x = std::max_element(dist, dist + n) - dist;
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// From x, find the max distance
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doBFS(x);
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auto* maxDistPtr = std::max_element(dist, dist + n);
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y = maxDistPtr - dist;
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distXY = *maxDistPtr;
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}
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std::vector<int> ret;
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int ptr = y;
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for (int i = 0; i < distXY / 2; ++i)
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ptr = father[ptr];
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ret.push_back(ptr);
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if (distXY & 1)
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ret.push_back(father[ptr]);
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return ret;
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}
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};
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int main() {
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auto ret = Solution::findMinHeightTrees(2, {{0, 1}});
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return 0;
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}
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