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  • POJ

    Catch That Cow

    Farmer John has been informed of the location of a fugitive cow and wants to catch her immediately. He starts at a point N (0 ≤ N ≤ 100,000) on a number line and the cow is at a point K (0 ≤ K ≤ 100,000) on the same number line. Farmer John has two modes of transportation: walking and teleporting.

    * Walking: FJ can move from any point X to the points - 1 or + 1 in a single minute
    * Teleporting: FJ can move from any point X to the point 2 × X in a single minute.

    If the cow, unaware of its pursuit, does not move at all, how long does it take for Farmer John to retrieve it?

    Input

    Line 1: Two space-separated integers: N and K

    Output

    Line 1: The least amount of time, in minutes, it takes for Farmer John to catch the fugitive cow.

    Sample Input

    5 17

    Sample Output

    4

    Hint

    The fastest way for Farmer John to reach the fugitive cow is to move along the following path: 5-10-9-18-17, which takes 4 minutes.
     
     
    开始考虑用dfs做。。没考虑双向问题,向左向右会陷入死循环。还是BFS大法好,,求最短路径问题,遍历部分点即可。
     
     
    #include<stdio.h>
    #include<queue>
    using namespace std;
    
    struct Node{
        int x,y;
    }node;
    int b[200010];
    
    int main()
    {
        int n,k;
        queue<Node> q;
        scanf("%d%d",&n,&k);
        if(n==k) printf("0
    ");    //特判
        else{
        node.x=n;
        node.y=0;
        q.push(node);
        b[n]=1;
        while(q.size()){
            node.x=q.front().x*2;
            node.y=q.front().y+1;
            if(node.x<=200010&&node.x>=0){
                if(node.x==k){
                    printf("%d
    ",node.y);
                    break;
                }
                if(b[node.x]==0){
                    b[node.x]=1;
                    q.push(node);
                }
            }
            node.x=q.front().x+1;
            node.y=q.front().y+1;
            if(node.x<=200010&&node.x>=0){
                if(node.x==k){
                    printf("%d
    ",node.y);
                    break;
                }
                if(b[node.x]==0){
                    b[node.x]=1;                
                    q.push(node);
                }
            }
            node.x=q.front().x-1;
            node.y=q.front().y+1;
            if(node.x<=200010&&node.x>=0){
                if(node.x==k){
                    printf("%d
    ",node.y);
                    break;
                }
                if(b[node.x]==0){
                    b[node.x]=1;                
                    q.push(node);
                }
            }
            q.pop();
        }
        }
        return 0;
    }
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  • 原文地址:https://www.cnblogs.com/yzm10/p/7230894.html
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