算法：bfs

此处bfs为外部循环（同floodfill），dfs会TLE。

#include <iostream>
#include <cstring>
#include <queue>
#include <cmath>
using namespace std;

#define in inline
#define rint register int
typedef long long LL;
typedef pair<int,int> PII;

in int read()
{
    rint x=0,f=0; register char ch=getchar();
    while(ch<'0'||ch>'9')f|=ch=='-',ch=getchar();
    while(ch>='0'&&ch<='9')x=(x<<3)+(x<<1)+(ch^48),ch=getchar();
    return f?-x:x;
}

/*----------code----------*/
const int N=1200010;
int dist[N];

int bfs(int n,int k)
{
    queue<int> q;
    q.push(n);
    
    memset(dist,-1,sizeof dist);
    dist[n]=0;
    
    while(!q.empty())
    {
        int t=q.front(); q.pop();
        if(t==k) return dist[k];
        
        rint ne[]={t*1.2,t+1,t-1};
        
        for(int i=0;i<3;i++)
            if(ne[i]<N&&dist[ne[i]]==-1)
            {
                q.push(ne[i]);
                dist[ne[i]]=dist[t]+1;
            }
    }
}

int main()
{
    int n,k; n=read(),k=read();
    
    cout<<bfs(n,k);
    
    return 0;
}

bfs模板题。

#include<bits/stdc++.h>
using namespace std;
struct node{
    int now;
    int dis;
};
int minv[1200005];
int main()
{
    int n,k; cin>>n>>k;
    for(int i=0;i<=1200000;i++) minv[i] = 9999999;
    queue<node> q;
    q.push((node){n,0});
    minv[n] = 0; 
    while(!q.empty())
    {
        node t = q.front();
        int nxt[3] ={t.now*1.2, t.now+1, t.now-1};
        for(int i=0;i<3;i++)
        {
            if(nxt[i]<= 1200000 && minv[nxt[i]] > t.dis+1)
            {
                minv[nxt[i]] = t.dis+1;
                q.push((node){nxt[i], t.dis+1}); 
            }
            if(nxt[i] == k)
            {
                cout<<t.dis+1<<endl;
                return 0;
            }
        }
        q.pop();
    }
    
    return 0; 
}