【广度优先遍历BFS】HDU-2717 Catch That Cow

注解

1、广度优先遍历BFS，三种情况：加一，减一，乘二。
2、注意边界！要先判断是否在[0,100000]范围，如果在，再判断是否访问过该位置。此顺序不能变化，否则会发生数组越界！导致ACCESS_VIOLATION。

代码

#include <iostream>
#include <queue>
#include <cstring>

using namespace std;

const int MAXN = 100001;

int N, K;
int visit[MAXN];

struct Node{
    int f;
    int step;
};

int bfs(){
    queue<Node> q;
    Node node;
    node.f = N;
    node.step = 0;
    visit[N] = 1;
    q.push(node);
    
    while(q.size()>0){
        Node top = q.front();
        q.pop();
        
        if(top.f==K){
            return top.step;
        }
        else{
            int step = top.step+1;
            int next1 = top.f + 1;
            int next2 = top.f - 1;
            int next3 = top.f * 2;
            if(next1<MAXN && visit[next1]==0){
                Node tmp;
                tmp.f = next1;
                tmp.step = step;
                q.push(tmp);
                visit[next1] = 1;
            }
            if(next2>=0 && visit[next2]==0){
                Node tmp;
                tmp.f = next2;
                tmp.step = step;
                q.push(tmp);
                visit[next2] = 1;
            }
            if(next3<MAXN && visit[next3]==0){
                Node tmp;
                tmp.f = next3;
                tmp.step = step;
                q.push(tmp);
                visit[next3] = 1;
            }
        }
    }
    
    return -1;
}

int main(){
    
    while(~scanf("%d %d", &N, &K)){
        memset(visit, 0, sizeof(visit));
        int ans = bfs();
        printf("%d\n", ans);
    }
    
    return 0;
}

结果