九度 题目1012：畅通工程 (BFS计算连通分支的个数)

用宽搜(bfs)计算图的连通分支的个数bfs_cnt。需要构建的道路的条数为bfs_cnt - 1

代码：

#include <iostream>#include <queue>using namespace std;int n, m, bfs_cnt;bool connect[1010][1010];bool vi[1010];queue<int> q;void init(){for (int i = 1; i <= n; ++ i){vi[i] = false;for (int j = 1; j <= n; ++ j){connect[i][j] = false;}}while (q.empty() == false) { q.pop();}bfs_cnt = 0;cin >> m;for (int i = 0; i < m; ++ i){int a, b;cin >> a >> b;connect[a][b] = connect[b][a] = true;}}void bfs(int index){++ bfs_cnt;q.push(index);while (q.empty() == false){int v = q.front();vi[v] = true;for (int j = 1; j <= n; ++ j){if (vi[j]==false && connect[v][j]){q.push(j);}}q.pop();}}int main(){while (cin >> n, n){init();for (int i = 1; i <= n; ++ i){if (vi[i] == false){bfs(i);}}cout << bfs_cnt - 1 << endl;}return 0;}