kuangbin_ShortPath D (POJ 3268)

#include <iostream>
#include <string>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <queue>
#include <map>
#include <vector>
#include <set>
#include <algorithm>
#define INF 0x3F3F3F3F
using namespace std;

typedef pair<int, int> pii;
struct cmp{
bool operator ()(const pii a, const pii b){
return a.first > b.first;
}
};

int size, head[1010], point[100010], next[100010], val[100010];

void init()
{
size = 0;
memset(head, -1, sizeof head);
}

void add(int from, int to, int value)
{
point[size] = to;
val[size] = value;
next[size] = head[from];
head[from] = size++;
}

void dij(int dis[], int s)
{
priority_queue <pii, vector<pii>, cmp> q;
q.push(make_pair(0, s));
dis[s] = 0;
while(!q.empty()){
pii u = q.top();
q.pop();
if(dis[u.second] < u.first) continue;
for(int i = head[u.second]; ~i; i = next[i]){
int j = point[i];
if(dis[j] > val[i] + u.first){
dis[j] = val[i] + u.first;
q.push(make_pair(dis[j], j));
}
}
}
}

int main()
{
int n, m, x;//parameter
int site1[100010], site2[100010], value[100010];//data
int dis1[1010], dis2[1010], ans;//result
//work out dis1
scanf("%d%d%d", &n, &m, &x);
memset(dis1, 0x3f, sizeof dis1);
memset(dis2, 0x3f, sizeof dis2);
init();
for(int i = 0; i < m; i++){
scanf("%d%d%d", &site1[i], &site2[i], &value[i]);
add(site1[i], site2[i], value[i]);
}
dij(dis1, x);
//work out dis2
init();
for(int i = 0; i < m; i++){
add(site2[i], site1[i], value[i]);
}
dij(dis2, x);
//output
ans = dis1[1] + dis2[1];
for(int i = 2; i <= n; i++){
ans = max(ans, dis1[i] + dis2[i]);
//printf("dis1[%d] = %d dis2[%d] = %d\n", i, dis1[i], i, dis2[i]);
}
printf("%d\n", ans);
return 0;
}