poj 3159 Candies (dij + heap)

3159 -- Candies

　　明明找的是差分约束，然后就找到这题不知道为什么是求1~n的最短路的题了。然后自己无聊写了一个heap，518ms通过。

代码如下：

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

 using namespace std;

 const int N = ;
 const int M = ;
 struct Edge {
     int t, nx, c;
 } edge[M];
 int eh[N], ec;

 void init() {
     memset(eh, -, sizeof(eh));
     ec = ;
 }

 void addedge(int s, int t, int c) {
     edge[ec].t = t, edge[ec].nx = eh[s], edge[ec].c = c;
     eh[s] = ec++;
 }

 struct Heap {
     int val[N], pos[N], id[N], sz, tmp, d;
     void init() {
         sz = ;
         memset(pos, -, sizeof(pos));
     }
     int up(int t) {
         while (t >  && val[t] < val[t >> ]) pos[id[t] = id[t >> ]] = t, swap(val[t], val[t >> ]), t >>= ;
         return t;
     }
     void push(int i, int v) {
         val[++sz] = v;
         pos[i] = up(sz);
         id[pos[i]] = i;
     }
     void down(int tmp) {
         while ((tmp << ) <= sz) {
             if (val[tmp] <= val[tmp << ] && val[tmp] <= val[tmp <<  | ]) break;
             if ((tmp <<  == sz) || val[tmp << ] <= val[tmp <<  | ]) {
                 d = tmp << ;
                 swap(pos[id[tmp]], pos[id[d]]);
                 swap(id[tmp], id[d]);
                 swap(val[tmp], val[d]);
                 tmp = d;
             } else {
                 d = tmp <<  | ;
                 swap(pos[id[tmp]], pos[id[d]]);
                 swap(id[tmp], id[d]);
                 swap(val[tmp], val[d]);
                 tmp = d;
             }
         }
     }
     void modify(int i, int v) {
         val[pos[i]] = v;
         down(pos[i]);
         pos[i] = up(pos[i]);
         id[pos[i]] = i;
     }
     void pop(int &i) {
         if (sz == ) {
             i = -;
             return ;
         }
         i = id[];
         pos[i] = -;
         if (sz == ) { sz--; return ;}
         val[] = val[sz];
         id[] = id[sz];
         pos[id[]] = ;
         sz--;
         if (sz > ) down();
     }
     int gv(int i) { return ~pos[i] ? val[pos[i]] : -;}
 } hp;
 int dis[N];

 int dij(int s, int t) {
     int cur, i;
     hp.init();
     memset(dis, , sizeof(dis));
     dis[s] = ;
     hp.push(s, );
     while (hp.sz) {
         hp.pop(cur);
         if (cur == t) return dis[cur];
         for (i = eh[cur]; ~i; i = edge[i].nx) {
             Edge &e = edge[i];
             if (dis[e.t] > dis[cur] + e.c) {
                 dis[e.t] = dis[cur] + e.c;
                 if (~hp.gv(e.t)) hp.modify(e.t, dis[e.t]);
                 else hp.push(e.t, dis[e.t]);
             }
         }
     }
     return -;
 }

 int main() {
     int x, y, v;
     int n, m;
     while (~scanf("%d%d", &n, &m)) {
         init();
         while (m--) {
             scanf("%d%d%d", &x, &y, &v);
             addedge(x, y, v);
         }
         printf("%d\n", dij(, n));
     }
     return ;
 }

——written by Lyon