poj 3278 Catch That Cow 广度优先搜索 + 回溯 队列 剪枝

#include<iostream>#include<stdio.h>#include<vector>using namespace std; int num;int sign=100000;//当kk>k的时候剪枝int n,k;bool c[100001];//记录是否已经使用过vector<int> test[2];//队列交替vector<int>::iterator t;int DFS();int main(){scanf("%d%d",&n,&k);if(n>=k){printf("%d",n-k);return 0;}num=0;test[num].push_back(n);c[n]=true;DFS();printf("%d",num);return 0;}int DFS(){int a=num%2;num++;if(sign<=num){num=sign;return 0;}int b=num%2;int kk;while(!test[a].empty()){kk=test[a].front(); t=test[a].begin();test[a].erase(t);if(k==kk-1||k==kk+1||k==kk*2){ return 0;}else if(kk>=k){if(kk-k+num<sign)sign=kk-k+num;} else {if(kk-1>=0&&kk-1<=100000&&!c[kk-1])test[b].push_back(kk-1),c[kk-1]=true; if(kk+1>=0&&kk+1<=100000&&!c[kk+1])test[b].push_back(kk+1),c[kk+1]=true; if(kk*2>=0&&kk*2<=100000&&!c[kk*2])test[b].push_back(kk*2),c[kk*2]=true;}}DFS();return 0;}

本程序优于第一个程序，0ms通过。第一个程序在队列删除元素上浪费大量时间。#include<iostream>#include<stdio.h>#include<vector>using namespace std; int num;int sign=100000;int x,y;int n,k;bool c[100001];vector<int> test[2];int DFS();int main(){scanf("%d%d",&n,&k);if(n>=k){printf("%d",n-k);return 0;}num=0;test[num].push_back(n);c[n]=true;DFS();printf("%d",num);return 0;}int DFS(){int a=num%2;num++;if(sign<=num){num=sign;return 0;}int b=num%2;int kk;int i;if(a==0)i=x;else i=y;while(i<test[a].size()){kk=test[a][i];i++; if(k==kk-1||k==kk+1||k==kk*2){ return 0;}else if(kk>=k){if(kk-k+num<sign)sign=kk-k+num;} else {if(kk-1>=0&&!c[kk-1])test[b].push_back(kk-1),c[kk-1]=true; if(kk+1<=100000&&!c[kk+1])test[b].push_back(kk+1),c[kk+1]=true; if(kk*2<=100000&&!c[kk*2])test[b].push_back(kk*2),c[kk*2]=true;}}if(a==0)x=i;else y=i;DFS();return 0;}

 

//本程序 0ms通过 队列不删除 删除费时 没有递归 不用标记属于第几层#include<iostream>#include<stdio.h>#include<vector>using namespace std; int num;int sign=100000;int n,k;bool c[100001];int f[100001];vector<int> test;int DFS();int main(){scanf("%d%d",&n,&k);if(n>=k){printf("%d",n-k);return 0;}num=0;test.push_back(n);f[n]=0;c[n]=true;DFS();printf("%d",f[k]);return 0;}int DFS(){ int kk;int i=0;while(i<test.size()){kk=test[i]; i++; if(kk-1>=0&&!c[kk-1])test.push_back(kk-1),c[kk-1]=true,f[kk-1]=f[kk]+1; if(kk+1<=100000&&!c[kk+1])test.push_back(kk+1),c[kk+1]=true,f[kk+1]=f[kk]+1;if(kk*2<=100000&&!c[kk*2])test.push_back(kk*2),c[kk*2]=true,f[kk*2]=f[kk]+1; } return 0;}

本人修改后的最有程序。0ms536k省时间省内存 两队列交替使用，随时清空从新使用，不记录已求出的最短时间（没有f数组）.#include<iostream>#include<stdio.h>#include<vector>using namespace std; int num;int sign=100000;int x,y;int n,k;bool c[100001];vector<int> test[2];int DFS();int main(){scanf("%d%d",&n,&k);if(n>=k){printf("%d",n-k);return 0;}num=0;test[num].push_back(n);c[n]=true;DFS();printf("%d",num);return 0;}int DFS(){int a=num%2;num++;if(sign<=num){num=sign;return 0;}int b=num%2;int kk;int i=0; while(i<test[a].size()){kk=test[a][i];i++; if(k==kk-1||k==kk+1||k==kk*2){ return 0;}else if(kk>=k){if(kk-k+num<sign)sign=kk-k+num;} else {if(kk-1>=0&&!c[kk-1])test[b].push_back(kk-1),c[kk-1]=true; if(kk+1<=100000&&!c[kk+1])test[b].push_back(kk+1),c[kk+1]=true; if(kk*2<=100000&&!c[kk*2])test[b].push_back(kk*2),c[kk*2]=true;}} test[a].clear();DFS();return 0;}