Dijkstra+Heap+前向星存图

一切尽在代码中。。。。。。。。

/*    dijkstra + heap，时间复杂度: O((n + e)log(n)).    对于稠密图来说，仍然是dij+heap快，而且越稠密越快!    用前向星来存图，空间复杂度为: O(m).    更新时间: 2011.09.22*/#include <iostream>#include <cstring>#include <cmath>#include <climits>#include <algorithm>#include <cstdio>using namespace std;typedef long long int64;#define mem(a, b) memset(a, b, sizeof(a))#define Sqr(x) ((x) * (x))template <class T>inline T Max(T a, T b) { if (a < b) a = b; return a; }template <class T>inline T Min(T a, T b) { if (a > b) a = b; return a; }template <class T>inline void Swap(T & a, T & b) { T dt = a; a = b; b = dt; }const int maxn = 50005;const int maxm = 50005 << 1; // 无向图.const double EPS = 1e-10;const int64 INF = (1LL << 60) + (1LL << 61);struct EDGE{    int a, b, c;    int next;};int n, m, ds, dt; // n个点，m条边，s为原点，t为终点。EDGE edge[maxm]; // 前向星.int edge_num;int first[maxn]; // 记录该点的第一条边在edge[]的下标.bool visited[maxn]; // 判断该点的最短路是否已经求出来了.int64 ans;struct Heap{ // 如果速度慢，就不要用struct，直接作为一般参数和函数.    int heapsize;    int heap_v[maxn]; // heap_v[i]为堆中第i个位置所存的图中的结点.int heap_map[maxn]; // heap_map[i]表示图中的点i在堆中的位置.int64 heap_w[maxn]; // heap_w[i]为堆中第i个位置所存的为dist[heap_v[i]].    void heap_swap(int i, int j)    {        Swap(heap_w[i], heap_w[j]);        heap_map[heap_v[i]] = j;        heap_map[heap_v[j]] = i;        Swap(heap_v[i], heap_v[j]);    }    void heap_up(int i)    {        while (i != 1)        {            if (heap_w[i] < heap_w[i >> 1])            {                heap_swap(i, i >> 1);                i >>= 1;            }            else break;        }    }    void heap_down(int i)    { // 注: 在dijkstra+heap没用到该函数.        while ((i << 1) <= heapsize)        {            i <<= 1;            if (i + 1 <= heapsize && heap_w[i + 1] < heap_w[i]) i++;            if (heap_w[i] < heap_w[i >> 1])            {                heap_swap(i, i >> 1);            }            else break;        }    }    void Delmin(void)    {        heap_swap(1, heapsize);        heapsize--;        heap_down(1);    }};Heap hp;void Init(void){    int i, j, k;    ans = 0; edge_num = 0;    mem(visited, 0);    fill(first, first + maxn, -1);    visited[ds] = 1;    for (i = 1; i <= n; i++)    {        hp.heap_v[i] = i;        hp.heap_map[i] = i;        hp.heap_w[i] = INF;    }    hp.heap_w[ds] = 0; hp.heapsize = n;    hp.heap_up(hp.heap_map[ds]);}void AddEdge(int a, int b, int c){    edge[edge_num].a = a, edge[edge_num].b = b, edge[edge_num].c = c;    edge[edge_num].next = first[a], first[a] = edge_num++;}void Dijkstra_heap(void){ // hp.heap_w[hp.heap_w[i]] 相当于 dist[i].    int i, j, k;    int t;    int64 temp;    for (t = 1; t < n; t++)    {        i = hp.heap_v[1];        temp = hp.heap_w[1]; // temp 相当于dist[i].        hp.Delmin();        visited[i] = 1;        if (visited[dt]) break; // 说明dist[dt]已经求出.        for (k = first[i]; k != -1; k = edge[k].next)        {            j = edge[k].b;            if (!visited[j] && temp + edge[k].c < hp.heap_w[hp.heap_map[j]])            {                hp.heap_w[hp.heap_map[j]] = temp + edge[k].c;                hp.heap_up(hp.heap_map[j]);            }        }    }}int main(void){//    freopen("Input.txt", "r", stdin);    int i, j;    int a, b, c;    while (scanf("%d %d %d %d", &n, &m, &ds, &dt) != EOF)    {        Init();        while (m--)        {            scanf("%d %d %d", &a, &b, &c);            AddEdge(a, b, c);//            AddEdge(b, a, c); // 无向图.        }        Dijkstra_heap();        ans = hp.heap_w[hp.heap_map[dt]];        if (ans == INF) cout << "Can't reach" << endl;        else cout << ans << endl;    }    return 0;}