[最短路] [洛谷] P1629 邮递员送信

非常巧妙的题目

最短路逆求所有点到本点距离

#pragma GCC optimize(2)
#include <cstdio>
#include <iostream>
#include <cstdlib>
#include <cmath>
#include <cctype>
#include <string>
#include <cstring>
#include <algorithm>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <ctime>
#include <vector>
#include <fstream>
#include <list>
#include <iomanip>
#include <numeric>
using namespace std;
typedef long long ll;

const int MAXN = 1e6 + 10;
const int INF = 0x3f3f3f3f;

ll next[MAXN], vsnext[MAXN], ans[MAXN], vsans[MAXN];

struct EDGE
{
	ll next, to, val;
}edge[MAXN], vsedge[MAXN];

int head[MAXN], vshead[MAXN];

int cnt = 0;

void add(int x, int y, int z)
{
	edge[++cnt].next = head[x];
	edge[cnt].val = z;
	edge[cnt].to = y;
	head[x] = cnt;
	vsedge[cnt].next = vshead[y];
	vsedge[cnt].val = z;
	vsedge[cnt].to = x;
	vshead[y] = cnt;
}

struct bfsnode
{
	ll now, dis;
	bfsnode(ll x, ll y)
	{
		now = x, dis = y;
	}
	bool operator < (const bfsnode &b) const
	{
		return this->dis > b.dis;
	}
};

bool finded[MAXN], vsfinded[MAXN];

void bfsone(bfsnode(x))
{
	priority_queue <bfsnode> PQ;
	PQ.push(x);
	while(!PQ.empty())
	{
		bfsnode B = PQ.top();
		PQ.pop();
		if(!finded[B.now])
		{
			finded[B.now] = true;
			ans[B.now] = min(ans[B.now], B.dis);
			for(int i = head[B.now]; i != 0; i = edge[i].next)
			{
				PQ.push(bfsnode(edge[i].to, B.dis + edge[i].val));
			}
		}
	}
}

void bfstwo(bfsnode(x))
{
	priority_queue <bfsnode> PQ1;
	PQ1.push(x);
	while(!PQ1.empty())
	{
		bfsnode B = PQ1.top();
		PQ1.pop();
		if(!vsfinded[B.now])
		{
			vsfinded[B.now] = true;
			vsans[B.now] = min(vsans[B.now], B.dis);
			for(int i = vshead[B.now]; i != 0; i = vsedge[i].next)
			{
				PQ1.push(bfsnode(vsedge[i].to, B.dis + vsedge[i].val));
			}
		}
	}
}

int main()
{
    ios::sync_with_stdio(false);

    cin.tie(0);     cout.tie(0);

    int n, m, x, y, z, sum = 0;

    cin>>n>>m;

    for(int i = 0; i <= n; i++)
    {
    	ans[i] = INF, vsans[i] = INF;
    }
    while(m--)
    {
    	cin>>x>>y>>z;
    	add(x, y, z);
    }

    bfsone(bfsnode(1, 0) );
    bfstwo(bfsnode(1, 0) );

    for(int i = 1; i <= n; i++)
    {
    	sum += (ans[i] + vsans[i]);
    }

    cout<<sum<<endl;
    return 0;
}