【搜索】Atcoder-ABC1873-C-Travel【全排列】

传送门

C - Travel

题意

寻找从起点1开始，经过所有点1次，再次回到起点1，权值总和为k次数。

思路

由于N(N<8)很小，枚举全排列即可。

AC代码

#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimization("unroll-loops")

#include<bits/stdc++.h>
using namespace std;

typedef long long ll;
const int INF = 0x3f3f3f3f;
const int mod = 1e9+7;
const int maxn =10;
                        
int a[maxn][maxn];
int b[maxn];
int n,k;
bool vis[maxn];
int ans = 0;
void dfs(int cnt){
	if(cnt>n){
        if(b[1]!=1) return ;
        int sum = 0;
		for(int i = 1; i <= n-1; i++){
            sum += a[b[i]][b[i+1]];
        }
        sum += a[b[n]][b[1]];
		if(sum==k) ans++;
		return ;
	}
	for(int i = 1; i <= n; i++){
		if(vis[i]==0){
			vis[i] = 1;
			b[cnt] = i;
			dfs(cnt+1);
			vis[i] = 0;
		}
	}
	return ;
}
int main(void){
    #ifndef ONLINE_JUDGE
    freopen("in.txt", "r", stdin);
    freopen("out.txt", "w", stdout);
    #endif
    cin >> n >> k;
    for(int i = 1; i <= n; i++){
        for(int j = 1; j <= n; j++){
            cin >> a[i][j];
        }
    }
    dfs(1);
    cout<<ans<<endl;
    return 0;
}