https://www.luogu.org/problemnew/show/P1546

题解：

/*
*@Author:   STZG
*@Language: C++
*/
#include <bits/stdc++.h>
#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<string>
#include<vector>
#include<bitset>
#include<queue>
#include<deque>
#include<stack>
#include<cmath>
#include<list>
#include<map>
#include<set>
//#define DEBUG
#define RI register int
using namespace std;
typedef long long ll;
//typedef __int128 lll;
const int N=100000+10;
const int M=100000+10;
const int MOD=1e9+7;
const double PI = acos(-1.0);
const double EXP = 1E-8;
const int INF = 0x3f3f3f3f;
int t,n,m,k,q;
int ans,cnt,flag,temp,sum;
int a[N];
char str;
struct node{
    int u,v,c;
    bool operator <(const node &S)const{
        return c<S.c;
    }
}e[N];
int pre[N];
int find(int x){
    if(x==pre[x])return x;
    return pre[x]=find(pre[x]);
}
int main()
{
#ifdef DEBUG
	freopen("input.in", "r", stdin);
	//freopen("output.out", "w", stdout);
#endif
    //ios::sync_with_stdio(false);
    //cin.tie(0);
    //cout.tie(0);
    //scanf("%d",&t);
    //while(t--){
    scanf("%d",&n);
    for(int i=1;i<=n;i++){
        for(int j=1;j<=n;j++){
            scanf("%d",&k);
            if(i>=j)
                continue;
            e[++cnt].u=i;
            e[cnt].v=j;
            e[cnt].c=k;
        }
    }
    sort(e+1,e+cnt+1);
    for(int i=1;i<=n;i++)
        pre[i]=i;
    for(int i=1;i<=cnt;i++){
        int tx=find(e[i].u);
        int ty=find(e[i].v);
        if(tx!=ty){
            pre[tx]=ty;
            ans+=e[i].c;
        }
    }
    cout<<ans<<endl;
    //}

#ifdef DEBUG
	printf("Time cost : %lf s\n",(double)clock()/CLOCKS_PER_SEC);
#endif
    //cout << "Hello world!" << endl;
    return 0;
}