C. Timofey and a tree 观察题 + dfs模拟
http://codeforces.com/contest/764/problem/C
题意:在n个顶点中随便删除一个,然后分成若干个连通子图,要求这若干个连通子图的颜色都只有一种。
记得边是双向的,wa15的可能是不知道边是双向的吧。
一个观察:如果某条边连接的两个顶点的颜色不同,那么可以看看删除这两个顶点,成立就成立,不成立就不成立。
因为必定要把这两个顶点分开。
然后就是暴力dfs了。
#include <cstdio> #include <cstdlib> #include <cstring> #include <cmath> #include <algorithm> #include <assert.h> #define IOS ios::sync_with_stdio(false) using namespace std; #define inf (0x3f3f3f3f) typedef long long int LL; #include <iostream> #include <sstream> #include <vector> #include <set> #include <map> #include <queue> #include <string> #include <bitset> const int maxn = 2e6 + 20; struct node { int u, v, tonext; }e[maxn]; int num; int first[maxn]; void add(int u, int v) { num++; e[num].u = u; e[num].v = v; e[num].tonext = first[u]; first[u] = num; } int c[maxn], in[maxn]; int u[maxn], v[maxn]; set<int>ss; int vis[maxn]; int DFN; int dfs(int cur, int no) { ss.insert(c[cur]); if (ss.size() >= 2) return false; bool flag = true; for (int i = first[cur]; i; i = e[i].tonext) { if (e[i].v == no) continue; if (vis[e[i].v] == DFN) continue; vis[e[i].v] = DFN; flag = flag && dfs(e[i].v, no); } return flag; } bool del(int cur) { for (int i = first[cur]; i; i = e[i].tonext) { ss.clear(); DFN++; vis[cur] = DFN; vis[e[i].v] = DFN; if (dfs(e[i].v, inf) == false) return false; } return true; } void work() { int n; cin >> n; for (int i = 1; i <= n - 1; ++i) { cin >> u[i] >> v[i]; } for (int i = 1; i <= n; ++i) { cin >> c[i]; } int which = inf; for (int i = 1; i <= n - 1; ++i) { if (c[u[i]] != c[v[i]] && which == inf) which = i; add(u[i], v[i]); add(v[i], u[i]); } if (which == inf) { cout << "YES" << endl; cout << 1 << endl; return; } // cout << which << " " << root << endl; if (del(u[which])) { cout << "YES" << endl; cout << u[which] << endl; return; } if (del(v[which])) { cout << "YES" << endl; cout << v[which] << endl; return; } cout << "NO" << endl; } int main() { #ifdef local freopen("data.txt", "r", stdin); // freopen("data.txt", "w", stdout); #endif work(); return 0; }
既然选择了远方,就要风雨兼程~
posted on 2017-02-04 00:56 stupid_one 阅读(128) 评论(0) 编辑 收藏 举报