poj 2395 Out of Hay、2485 Highways（求最小生成树的最长边）

 

两道题都是求最小生成树的最长边。

poj 2395 Out of Hay

 http://poj.org/problem?id=2395

kruskal实现：

#include "stdio.h" #include "string.h" #include "algorithm" #include "iostream" using namespace std; const int INF = 1e9, MAX = 2001; int fa[MAX]; struct edge { int s, e, val; }; edge edges[10001]; bool cmp(edge a, edge b) { return a.val < b.val; } int getfather(int x) { if(x != fa[x]) fa[x] = getfather(fa[x]); return fa[x]; } int kruskal(int nv, int ne) { int i, t, ans = 0; for(i = 1; i <= nv; i++) { fa[i] = i; } sort(edges + 1, edges + ne + 1, cmp); for(i = 1, t = 1; t < nv; i++) { int fa1 = getfather(edges[i].s); int fa2 = getfather(edges[i].e); if(fa1 != fa2) { fa[fa1] = fa2; t++; if(edges[i].val > ans) ans = edges[i].val; } } return ans; } int main() { int nv, ne, i; while(scanf("%d%d", &nv, &ne) != EOF) { for(i = 1; i <= ne; i++) { scanf("%d%d%d", &edges[i].s, &edges[i].e, &edges[i].val); } cout << kruskal(nv, ne) << endl; } return 0; }

 

poj 2485 Highways

http://poj.org/problem?id=2485

prim实现：

<pre class="cpp" name="code">#include "cstdio" #include "iostream" using namespace std; int g[500][500]; const int INF = 100000000; int min(int a, int b) { return a < b? a : b; } int prim(int nv) { int i, j, dis[500], ans = -1; bool vis[500]; for(i = 0; i < nv; i++) { dis[i] = INF; vis[i] = false; } int now, next = 0; for(i = 0; i + 1< nv; i++) { now = next; vis[now] = true; for(j = 0; j < nv; j++) { if(!vis[j]) { dis[j] = min(dis[j], g[now][j]); } } int minval = INF; for(j = 0; j < nv; j++) { if(!vis[j] && minval > dis[j]) { minval = dis[j]; next = j; } } if(minval > ans) ans = minval; } return ans; } int main() { int n, T, i, j; cin >> T; while(T--) { cin >> n; for(i = 0; i < n; i++) for(j = 0; j < n; j++) cin >> g[i][j]; cout << prim(n) << endl; } return 0; }