poj 3159 Candies

差分约束。

 

需要优化，SPFA+queue TLE了 = =。。。SPFA+stack 700+MS，Dijkstra + priority_queue 500MS..

 

以前没用过栈，记得就用过一次WA了，以后再也没用过。这次就把队列改成栈，Q.front() 改成Q.top()就过了，仰慕啊。。。

 

用邻接表越来越顺啦，(*^__^*) 嘻嘻……

 

这题是建图后求1到N的最大距离。以1为源点。建图后求最短路即可。

 

SPFA+stack

#include <cstdio>#include <cstdlib>#include <iostream>#include <string.h>#include <queue>#include <limits.h>#include <stack>#define MAX 30010using namespace std;typedef struct CANDY{int to,len;CANDY *next;}CANDDY;CANDY *kid[MAX],node[MAX*10];int cou,n;void init(){memset(kid,'/0',sizeof(kid));memset(node,'/0',sizeof(node));cou = 0;}int SPFA(){stack<int> Q;int i,len,to,x,inq[MAX],dis[MAX];CANDY *head;memset(inq,0,sizeof(inq));for(i=0; i<=n; i++)dis[i] = INT_MAX;dis[1] = 0;inq[1] = 1;Q.push(1);while( !Q.empty() ){x = Q.top();Q.pop();inq[x] = 0;head = kid[x];while( head != NULL ){to = head->to;len = head->len;if( dis[to] > dis[x] + len ){dis[to] = dis[x] + len;if( !inq[to] ){inq[to] = 1;Q.push(to);}}head = head->next;}}return dis[n];}void Add(int u,int v,int len){node[cou].to = v;node[cou].len = len;node[cou].next = kid[u];kid[u] = &node[cou++];}int main(){int from,to,len,m,ans,i;while( scanf("%d%d",&n,&m) != EOF ){init();while( m-- ){scanf("%d%d%d",&from,&to,&len);Add(from,to,len);}ans = SPFA();printf("%d/n",ans);}return 0;} 

 

Dijkstra+priority_queue

#include <cstdio>#include <cstdlib>#include <iostream>#include <string.h>#include <queue>#include <limits.h>#define MAX 30010using namespace std;typedef struct CANDY{int to,len;int num; CANDY *next;}CANDDY;CANDY *kid[MAX],node[MAX*10];typedef struct DIS{int len,num;}DIS;int cou,n;void init(){memset(kid,'/0',sizeof(kid));memset(node,'/0',sizeof(node));cou = 0;}bool operator<(DIS a,DIS b){return a.len > b.len;}priority_queue <DIS> Q;int Dijkstra(){while( !Q.empty() )Q.pop(); int i,k,used[MAX],now,len,to;DIS dis[MAX],tmp;CANDY *head;memset(used,0,sizeof(used));for(i=1; i<=n; i++){dis[i].num = i;dis[i].len = INT_MAX;}dis[1].len = 0;dis[1].num = 1;Q.push(dis[1]);while( !Q.empty() ){tmp = Q.top();Q.pop();now = tmp.num;if( used[now] == 1 )continue;used[now] = 1;head = kid[now];while( head != NULL ){len = head->len;to = head->to;if( dis[to].len > dis[now].len + len ){dis[to].len = dis[now].len + len;Q.push(dis[to]);}head = head->next;}}return dis[n].len;}void Add(int u,int v,int len){node[cou].to = v;node[cou].len = len;node[cou].next = kid[u];kid[u] = &node[cou++];}int main(){int from,to,len,m,ans,i;while( scanf("%d%d",&n,&m) != EOF ){init();while( m-- ){scanf("%d%d%d",&from,&to,&len);Add(from,to,len);}ans = Dijkstra();printf("%d/n",ans);}return 0;}