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 = 50005;
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 = 0; i < N; i++) {
        scanf("%d%d", &A[i].in, &A[i].out);
        A[i].pos = i;
        if (A[i].in == 1) {
            pre[i] = -1;
            vis[i] = true;
            Q.push(A[i]);
        }
    }

    if (K == 1) {
        printf("1
1
");
    } else {
        if (Q.empty()) {
            printf("-1
");
        } else {
            while (!Q.empty()) {
                Link front = Q.front();
                if (front.out == K) {
                    break;
                }
                for (int i = 0; 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
");
            } else {
                int cnt = 0;
                int i = Q.front().pos;
                for (;-1 != pre[i];) {
                    B[cnt++] = A[i].out;
                    i = A[pre[i]].pos;
                }
                B[cnt++] = A[i].out;

                printf("%d
1
", cnt+1);
                for (int k = cnt-1; k >= 0; k--) {
                    printf("%d
", B[k]);
                } 
            }
        }
    }
    
} 

　　看到别人用SPFA、dijkstra,有时间也试一试！

　　【待写】