ZR#1012

## ZR#1012

解法：

CODE:

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<queue>

using namespace std;

#define INF 2147483647
const int N = 1e6 + 100;

int dis[N],x,n;
bool vis[N];
queue<int> q;

inline void calc(int v,int u,int val) {
    if(dis[v] > dis[u] + val) {
        dis[v] = dis[u] + val;
        if(!vis[v]) q.push(v),vis[v] = true;
    }
}
inline void spfa() {
    while(!q.empty()) {
        int v = q.front();
        q.pop();
        if(v < n) calc(v + 1,v,1);
        if(v > 0) {
            calc(v - 1,v,1);
            for(int i = 1 ; v * i <= n ; i++) {
                if(v * (i + 1) > n) calc(n,v,2 * i + 4 + v * (i + 1) - n);
                else calc(v * (i + 1),v,2 * i + 4);
            }
        }
        vis[v] = false;
    }
}

int main() {
    scanf("%d%d",&x,&n);
    for(int i = 0 ; i <= n ; i++) dis[i] = INF;
    if(x > n) {
        dis[0] = 3,dis[n] = x - n;
        vis[x] = vis[n] = vis[0] = true;
        q.push(0);
        q.push(n);
    } else {
        dis[x] = 0;
        vis[x] = 1;
        q.push(x);
    }
    spfa();
    printf("%d\n",dis[n]);
    //system("pause");
    return 0;
}