UVA 10938 - Flea circus(dfs)

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UVA 10938 - Flea circus

题目链接

题意：给定一棵树，然后每次询问两个点，问沿这两点路径走两点会相遇还是会穿过

思路：每次询问，进行一次dfs，由于是一棵树，所以每个结点只需要遍历一遍就能找出路径了，记录下路径输出即可

代码:

#include <cstdio>#include <cstring>#include <vector>#include <algorithm>using namespace std;const int N = 5005;int n, path[N], pn;vector<int> g[N];bool dfs(int u, int e, int fa) {path[pn++] = u;if (u == e) return true;for (int i = 0; i < g[u].size(); i++) {int v = g[u][i];if (fa == v) continue;if (dfs(v, e, u)) return true;}pn--;return false;}int main() {while (~scanf("%d", &n) && n) {for (int i = 1; i <= n; i++)g[i].clear();int u, v;for (int i = 0; i < n - 1; i++) {scanf("%d%d", &u, &v);g[u].push_back(v);g[v].push_back(u);}int q;scanf("%d", &q);int s, e;while (q--) {scanf("%d%d", &s, &e);pn = 0;dfs(s, e, -1);if (pn % 2) printf("The fleas meet at %d.\n", path[pn / 2]);else {int a = path[pn / 2 - 1], b = path[pn / 2];if (a > b) swap(a, b);printf("The fleas jump forever between %d and %d.\n", a, b);}}}return 0;}

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