HDU-1688-Sightseeing

描述

题解

代码

#include <iostream>
#include <cstring>
#include <algorithm>
#include <queue>
#include <vector>
#include <cstdio>

using namespace std;

const int INF = 0x3f3f3f3f;
const int MAXN = 1010;

struct Edge
{
int to, w;
};

struct node
{
int v, dist;
int tag;
bool friend operator < (const node &a, const node &b)
{
if (a.dist != b.dist)
{
return a.dist > b.dist;
}
return a.v > b.v;
}
};

priority_queue<node> Q;
vector<Edge> graph[MAXN];

int cnt[MAXN][3];   //  cnt[v][1]存储最短路径数，cnt[v][2]存储次短路径数
int vis[MAXN][3];   //  同理，vis存状态
int dis[MAXN][3];   //  dis[v][1]存储最短，dis[v][2]存储次短
int N, M, A, B, L;

void init()
{
for (int i = 0; i < MAXN; i++)
{
cnt[i][1] = cnt[i][2] = 0;
vis[i][1] = vis[i][2] = 0;
dis[i][1] = dis[i][2] = INF;
}
}

void Dijstra(int st, int ed)
{
dis[st][1] = 0;
cnt[st][1] = 1;
node q, p;
p.dist = 0;
p.tag = 1;
p.v = st;
Q.push(p);
while (!Q.empty())
{
q = Q.top();
Q.pop();
if (vis[q.v][q.tag])
{
continue;
}
vis[q.v][q.tag] = 1;
for (int i = 0; i < graph[q.v].size(); i++)
{
int v = graph[q.v][i].to;
int w = graph[q.v][i].w;
//  找到一条比“最短”更短的路
if (!vis[v][1] && dis[v][1] > q.dist + w)
{
//  把“最短“变为”次短“
if (dis[v][1] != INF)
{
dis[v][2] = dis[v][1];
cnt[v][2] = cnt[v][1];
p.dist = dis[v][2];
p.tag = 2;
p.v = v;
Q.push(p);
}
//  更新”最短“
dis[v][1] = q.dist + w;
cnt[v][1] = cnt[q.v][q.tag];
p.tag = 1;
p.dist = dis[v][1];
p.v = v;
Q.push(p);
}
//  找到一条”最短“，更新”最短条数“
else if (!vis[v][1] && dis[v][1] == q.dist + w)
{
cnt[v][1] += cnt[q.v][q.tag];
}
//  找到一条比”最短“长，比”次短“短的路，更新”次短“
else if (!vis[v][2] && dis[v][2] > q.dist + w)
{
dis[v][2] = q.dist + w;
cnt[v][2] = cnt[q.v][q.tag];
p.tag = 2;
p.dist = dis[v][2];
p.v = v;
Q.push(p);
}
//  找到一条”次短“，更新”次短条数“
else if (!vis[v][2] && dis[v][2] == q.dist + w)
{
cnt[v][2] += cnt[q.v][q.tag];
}
}
}
}

int main()
{
int T;
scanf("%d", &T);

Edge temp;
int st, ed;
while (T--)
{
init();
for (int i = 0; i < MAXN; i++)
{
graph[i].clear();
}

scanf("%d%d", &N, &M);
for (int i = 0; i < M; i++)
{
scanf("%d%d%d", &A, &B, &L);
temp.to = B;
temp.w = L;
graph[A].push_back(temp);
}

scanf("%d%d", &st, &ed);

Dijstra(st, ed);

if (dis[ed][1] + 1 == dis[ed][2])
{
printf("%d\n", cnt[ed][1] + cnt[ed][2]);
}
else
{
printf("%d\n", cnt[ed][1]);
}
}
return 0;
}

参考