POJ 3278 Catch That Cow

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
#define CL(x, y) memset(x,y,sizeof(x))
using namespace std;
const int MAX = 200005;//100005太小了？？use[]越界
int a, b, i, j, temp;
int used[MAX];
void BFS(int x, int y);
struct node
{
    int num;
    int step;
};
queue <node> Q;
int main()
{
    while(cin >> a >> b)
    {
        CL(used, 0);
        BFS(a, b);
    }
    return 0;
}
void BFS(int front, int rear)
{
    while(!Q.empty())
        Q.pop();//Q.clear();清空
    node first, cur, next;
    first.num = front;
    first.step = 0;
    used[front] = 1;
    Q.push(first);
    while(!Q.empty())
    {
        cur = Q.front();
        Q.pop();
        if(cur.num == rear)
        {
            cout << cur.step << endl;
            return ;
        }
        for(j = 0; j < 3; j++)
        {
            if(j == 0)
                temp = cur.num-1;
            else if(j == 1)
                temp = cur.num+1;
            else
                temp = cur.num*2;
            //            cout << temp << endl;
            if(!used[temp] && temp>=0 && temp <= 100000)
            {
                next.num = temp;
                next.step = cur.step+1;
                used[temp] = 1;
//                cout << next.num << " " << next.step << endl;
                Q.push(next);
                Q.push(next);
            }
        }
    }
}

Runtime Error可能是数组过小，特别是used[]数组，最后一定不可以越界