「 Luogu P2196 」 挖地雷

# 解题思路

跑 $\text{n}$ 遍 $\text{spfa}$ 并记录路径，找到比当前最长路长的就更新答案，并且将路径也更新，注意起点的处理。

 

# 附上代码

#include <iostream>
#include <cstring>
#include <cstdio>
#include <queue>
#define INF 123456789
using namespace std;
int n, a[23], head[23], cnt, pre[23], Ans, ans[23], dis[23], TANS[23], t;
bool vis[23];
queue<int> Q;
struct edge {
    int nxt, u, v, w;
}ed[23*23];
inline void addedge(int x, int y, int z) {
    ed[++cnt].nxt = head[x];
    head[x] = cnt;
    ed[cnt].u = x, ed[cnt].v = y, ed[cnt].w = z;
}
inline int spfa(int s) {
    while (!Q.empty()) Q.pop();
    memset(vis, 0, sizeof(vis));
    for(int i=1; i<=n; i++) dis[i] = -INF;
    Q.push(s), dis[s] = a[s], vis[s] = 1, pre[s] = 0;
    while (!Q.empty()) {
        int u = Q.front(); Q.pop();
        for(int i=head[u]; i; i=ed[i].nxt) {
            if(dis[ed[i].v] < dis[u] + ed[i].w) {
                dis[ed[i].v] = dis[u] + ed[i].w;
                pre[ed[i].v] = u;
                if(!vis[ed[i].v])
                    vis[ed[i].v] = 1, Q.push(ed[i].v);
            }
        }
        vis[u] = 0;
    }
    for(int i=1; i<=n; i++) {
        if(dis[i] > Ans) {
            Ans = dis[i];
            for(int j=1; j<=n; j++) ans[j] = pre[j];
            t = i;
        }
    }
}
int main() {
    scanf("%d", &n);
    int x;
    for(int i=1; i<=n; i++) scanf("%d", &a[i]);
    for(int i=1; i<=n; i++) {
        for(int j=i+1; j<=n; j++) {
            scanf("%d", &x);
            if(x == 1) addedge(i, j, a[j]);
        }
    }
    for(int i=1; i<=n; i++)
        spfa(i);
    cnt = 0;
    for(int i=t; i; i=ans[i]) TANS[++cnt] = i;
    for(int i=cnt; i>=1; i--) printf("%d ", TANS[i]);
    printf("\n%d", Ans);
}