【HDOJ】2717 Catch That Cow

bfs。

/* 2717 */
#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <queue>
using namespace std;

#define MAXN 100001

queue<int> Q;
int s[MAXN];
int n, k;
int ans;

void bfs() {
    int cur, nxt;
    
    while (!Q.empty())
        Q.pop();
    
    memset(s, 0, sizeof(s));
    
    Q.push(n);
    while (!Q.empty()) {
        cur = Q.front();
        Q.pop();
        if (cur == k)
            break;
        nxt = cur - 1;
        if (nxt>=0 && s[nxt]==0) {
            Q.push(nxt);
            s[nxt] = s[cur] + 1;
        }
        nxt = cur + 1;
        if (nxt<MAXN && s[nxt]==0) {
            Q.push(nxt);
            s[nxt] = s[cur] + 1;
        }
        nxt = cur + cur;
        if (nxt<MAXN && (nxt-k)<(k-cur) && s[nxt]==0) {
            Q.push(nxt);
            s[nxt] = s[cur] + 1;
        }
    }
}

int main() {

#ifndef ONLINE_JUDGE
    freopen("data.in", "r", stdin);
#endif

    while (scanf("%d %d", &n, &k) != EOF) {
        if (n >= k)
            printf("%d
", n-k);
        else {
            bfs();
            printf("%d
", s[k]);
        }
    }

    return 0;
}