数组要开大，不然会RE
#include<bits/stdc++.h> using namespace std; int a[10000005]; int n,k; struct node { int x, step; }; queue<node> q; void bfs(int x){ a[x] = 1; q.push((node){x,0}); while(!q.empty()){ node front = q.front(); q.pop(); if(front.x == k){ cout << front.step; return; } int nt = front.step + 1; int nx = front.x + 1; if(!a[nx] && nx >= 0 && nx <= 100000){ a[nx] = 1; q.push((node){nx, nt}); } nx = front.x - 1; if(!a[nx] && nx >= 0 && nx <= 100000){ a[nx] = 1; q.push((node){nx, nt}); } nx = front.x * 2; if(!a[nx] && nx >= 0 && nx <= 100000){ a[nx] = 1; q.push((node){nx, nt}); } } } int main(){ cin >> n >> k; bfs(n); }