HDU 4514 湫湫系列故事――设计风景线 (树形DP)
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题意:略。
析:首先先判环,如果有环直接输出,用并查集就好,如果没有环,那么就是一棵树,然后最长的就是树的直径,这个题注意少开内存,容易超内存,
还有用C++交用的少一些,我用G++交的卡在32764K,限制是32768K。。
代码如下:
#pragma comment(linker, "/STACK:1024000000,1024000000") #include <cstdio> #include <string> #include <cstdlib> #include <cmath> #include <iostream> #include <cstring> #include <set> #include <queue> #include <algorithm> #include <vector> #include <map> #include <cctype> #include <cmath> #include <stack> //#include <tr1/unordered_map> #define freopenr freopen("in.txt", "r", stdin) #define freopenw freopen("out.txt", "w", stdout) using namespace std; //using namespace std :: tr1; typedef long long LL; typedef pair<int, int> P; const int INF = 0x3f3f3f3f; const double inf = 0x3f3f3f3f3f3f; const LL LNF = 0x3f3f3f3f3f3f; const double PI = acos(-1.0); const double eps = 1e-8; const int maxn = 1e5 + 5; const LL mod = 10000000000007; const int N = 1e6 + 5; const int dr[] = {-1, 0, 1, 0, 1, 1, -1, -1}; const int dc[] = {0, 1, 0, -1, 1, -1, 1, -1}; const char *Hex[] = {"0000", "0001", "0010", "0011", "0100", "0101", "0110", "0111", "1000", "1001", "1010", "1011", "1100", "1101", "1110", "1111"}; inline LL gcd(LL a, LL b){ return b == 0 ? a : gcd(b, a%b); } int n, m; const int mon[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}; const int monn[] = {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}; inline int Min(int a, int b){ return a < b ? a : b; } inline int Max(int a, int b){ return a > b ? a : b; } inline LL Min(LL a, LL b){ return a < b ? a : b; } inline LL Max(LL a, LL b){ return a > b ? a : b; } inline bool is_in(int r, int c){ return r >= 0 && r < n && c >= 0 && c < m; } vector<P> G[maxn]; int p[maxn], dp[maxn]; bool vis[maxn], viss[maxn]; int Find(int x){ return x == p[x] ? x : p[x] = Find(p[x]); } int bfs(int root){ memset(vis, false, sizeof vis); memset(dp, 0, sizeof dp); queue<int> q; q.push(root); vis[root] = viss[root] = true; int ans = root, maxx = 0; while(!q.empty()){ int u = q.front(); q.pop(); for(int i = 0; i < G[u].size(); ++i){ P p = G[u][i]; int v = p.first; int w = p.second; if(vis[v]) continue; vis[v] = viss[v] = true; dp[v] = dp[u] + w; if(maxx < dp[v]){ maxx = dp[v]; ans = v; } q.push(v); } } return ans; } int solve(int root){ int u = bfs(root); int v = bfs(u); return dp[v]; } int main(){ while(scanf("%d %d", &n, &m) == 2){ int u, v, c; for(int i = 1; i <= n; ++i) G[i].clear(), p[i] = i; bool ok = false; for(int i = 0; i < m; ++i){ scanf("%d %d %d", &u, &v, &c); int x = Find(u); int y = Find(v); if(x != y) p[y] = x; else ok = true; G[u].push_back(P(v, c)); G[v].push_back(P(u, c)); } if(ok){ puts("YES"); continue; } memset(viss, false, sizeof viss); int ans = 0; for(int i = 1; i <= n; ++i) if(!viss[i]) ans = Max(ans , solve(i)); printf("%d\n", ans); } return 0; }
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