?prim：
給出一個無向圖，求出最小生成樹，如果該圖不連通，則輸出impossible。

#include<bits/stdc++.h> using namespace std; const int maxm = 200005; const int inf = 0x3f3f3f3f; struct edge{int v, w, next; }e[maxm << 1]; int cnt, n, m, sum, t, p, now = 1; int dis[5005], head[maxm], vis[5005]; int a, b, c;void add(int uu, int vv, int ww) {e[++cnt].v = vv;e[cnt].w = ww;e[cnt].next = head[uu];head[uu] = cnt; } int main() {cin >> n >> m;for(int i = 1; i <= m; i++){cin >> a >> b >> c;add(a, b, c); add(b, a, c);}for(int i = 1; i <= n; i++)dis[i] = inf;for(int i = head[1]; i; i = e[i].next)dis[e[i].v] = min(e[i].w, dis[e[i].v]);while(++t < n){vis[now] = 1;int minn = inf;now = -1;for(int i = 1; i <= n; i++){if(!vis[i] && minn > dis[i]){minn = dis[i];now = i;}}if(now == -1) {cout << "impossible";return 0;}sum += minn;for(int i = head[now]; i; i = e[i].next){if(!vis[e[i].v] && e[i].w < dis[e[i].v])dis[e[i].v] = e[i].w;}}cout << sum;return 0; }

?

給出一個無向圖，求出最小生成樹。不用判斷是否連通

#include<bits/stdc++.h> using namespace std; const int maxm = 200005; const int inf = 0x3f3f3f3f; struct edge{int v, w, next; }e[maxm << 1]; int cnt, n, m, sum, t, p, now = 1; int dis[5005], head[maxm], vis[5005]; int a, b, c;void add(int uu, int vv, int ww) {e[++cnt].v = vv;e[cnt].w = ww;e[cnt].next = head[uu];head[uu] = cnt; } int main() {cin >> n >> m;for(int i = 1; i <= m; i++){cin >> a >> b >> c;add(a, b, c); add(b, a, c);}for(int i = 1; i <= n; i++)dis[i] = inf;for(int i = head[1]; i; i = e[i].next)dis[e[i].v] = min(e[i].w, dis[e[i].v]);while(++t < n){vis[now] = 1;int minn = inf;for(int i = 1; i <= n; i++){if(!vis[i] && minn > dis[i]){minn = dis[i];now = i;}}if(dis[now] == inf) {cout << "orz";return 0;}sum += minn;for(int i = head[now]; i; i = e[i].next){if(!vis[e[i].v] && e[i].w < dis[e[i].v])dis[e[i].v] = e[i].w;}}cout << sum;return 0; }

兩者差別在于每次循環邊時對now的處理

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轉載于:https://www.cnblogs.com/lovezxy520/p/11615273.html

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