POJ1789《Truck History》方法：Prim

以序列字符的不同数为边权，求一颗最小生成树，这里注意松弛操作与Dijkstra的区别。

Prim: if (!v[j] && dis[j] > w[s][j]) 

Dijkstra: if (!v[j] && dis[j] > dis[s] + w[s][j]) 

#include <iostream>#include <cstdio>#include <cstring>using namespace std;const int inf = 100; // 距离范围1到7int n; //种类char str[2001][8];int w[2001][2001]; //点到点距离，边权int dis[2001]; //离源点距离bool v[2001]; //visitedint distance(char *a, char *b){int cnt = 0;for (int i = 0; i < 7; ++i) if (a[i] != b[i])++cnt;return cnt;}void prim(){memset(v, 0, sizeof(v));int s = 1, sum = 0;dis[s] = 0; //选1号点为根v[s] = true;for (int i = 2; i <= n; ++i) {dis[i] = w[i][1];}for (int i = 1; i <= n-1; ++i) { //将剩余点依次加入树中，即可//选取书外,dis最小的点int min = inf;for (int j = 1; j <= n; ++j) {if (!v[j] && dis[j] < min) {min = dis[j];s = j; }}v[s] = true;sum += min;for (int j = 1; j <= n; ++j)if (!v[j] && dis[j] > w[s][j]) // 对剩下的点松弛，这里的松弛并非用Dijkstra的dis[i] > dis[s] + w[s][j]dis[j] = w[s][j];}cout << "The highest possible quality is 1/" << sum << '.' << endl;}int main(){//freopen("temp.txt", "r", stdin);while (cin >> n && n) {for (int i = 1; i <= n; ++i) cin >> str[i];for (int i = 1; i <= n-1; ++i) for (int j = i+1; j <= n; ++j) w[i][j] = w[j][i] = distance(str[i], str[j]);prim();}return 0;}