POJ 2457 Part Acquisition

　　第一反应是BFS,比较直观，但是输出路径写的不是很熟练，此外，习惯不好，“==”写成了“=”，所以常量一定放前面！

 #include <cstdio>
 #include <queue>
 #include <cstring>
 using namespace std;
 int N, K;
 typedef struct node
 {
     int in, out;
     int pos;
 }Link;
 const int maxn = ;
 bool vis[maxn];
 Link A[maxn];
 int pre[maxn], B[maxn];

 int main(void) {
     freopen("in.txt", "r", stdin);
     freopen("out.txt", "w", stdout);
     scanf("%d%d", &N, &K);
     memset(vis, false, sizeof(vis));
     queue<Link> Q;
     for (int i = ; i < N; i++) {
         scanf("%d%d", &A[i].in, &A[i].out);
         A[i].pos = i;
         if (A[i].in == ) {
             pre[i] = -;
             vis[i] = true;
             Q.push(A[i]);
         }
     }

     if (K == ) {
         printf("1\n1\n");
     } else {
         if (Q.empty()) {
             printf("-1\n");
         } else {
             while (!Q.empty()) {
                 Link front = Q.front();
                 if (front.out == K) {
                     break;
                 }
                 for (int i = ; i < N; i++) {
                     if (!vis[i] && A[i].in == front.out) {
                         Q.push(A[i]);
                         vis[i] = true;
                         pre[i] = front.pos;
                     }
                 }
                 Q.pop();

             }
             if (Q.empty()) {
                 printf("-1\n");
             } else {
                 int cnt = ;
                 int i = Q.front().pos;
                 for (;- != pre[i];) {
                     B[cnt++] = A[i].out;
                     i = A[pre[i]].pos;
                 }
                 B[cnt++] = A[i].out;

                 printf("%d\n1\n", cnt+);
                 for (int k = cnt-; k >= ; k--) {
                     printf("%d\n", B[k]);
                 }
             }
         }
     }

 } 

　　看到别人用SPFA、dijkstra,有时间也试一试！

　　【待写】