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 = 33333;
const int M = 155555;
struct Edge {
    int t, nx, c;
} edge[M];
int eh[N], ec;

void init() {
    memset(eh, -1, sizeof(eh));
    ec = 0;
}

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 = 0;
        memset(pos, -1, sizeof(pos));
    }
    int up(int t) {
        while (t > 1 && val[t] < val[t >> 1]) pos[id[t] = id[t >> 1]] = t, swap(val[t], val[t >> 1]), t >>= 1;
        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 << 1) <= sz) {
            if (val[tmp] <= val[tmp << 1] && val[tmp] <= val[tmp << 1 | 1]) break;
            if ((tmp << 1 == sz) || val[tmp << 1] <= val[tmp << 1 | 1]) {
                d = tmp << 1;
                swap(pos[id[tmp]], pos[id[d]]);
                swap(id[tmp], id[d]);
                swap(val[tmp], val[d]);
                tmp = d;
            } else {
                d = tmp << 1 | 1;
                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 == 0) {
            i = -1;
            return ;
        }
        i = id[1];
        pos[i] = -1;
        if (sz == 1) { sz--; return ;}
        val[1] = val[sz];
        id[1] = id[sz];
        pos[id[1]] = 1;
        sz--;
        if (sz > 0) down(1);
    }
    int gv(int i) { return ~pos[i] ? val[pos[i]] : -1;}
} hp;
int dis[N];

int dij(int s, int t) {
    int cur, i;
    hp.init();
    memset(dis, 127, sizeof(dis));
    dis[s] = 0;
    hp.push(s, 0);
    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 -1;
}

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
", dij(1, n));
    }
    return 0;
}

——written by Lyon