题目链接：http://poj.org/problem?id=3278
分析：广搜，每次三种情况枚举一下，太水不多说了。
#include <cstdio> #include <cstring> #include <cmath> #include <iostream> #include <algorithm> #include <queue> #include <cstdlib> #include <vector> #include <set> #include <map> #define LL long long #define mod 1000000007 #define inf 0x3f3f3f3f #define N 100010 using namespace std; struct node { int x,step; bool operator<(const node a)const { return step>a.step; } }; priority_queue<node>que; int vis[N]; int judge(int x) { return x>=0&&x<=100000; } node make_node(int a,int b) { node temp; temp.x=a;temp.step=b; return temp; } int main() { int n,k; while(scanf("%d%d",&n,&k)>0) { memset(vis,0,sizeof(vis)); while(!que.empty())que.pop(); que.push(make_node(n,0)); vis[n]=1; int ans=0; while(!que.empty()) { node now=que.top(); que.pop(); int x=now.x;//printf("%d %d ",now.x,now.step); if(x==k) { ans=now.step; break; } if(judge(x+1)&&!vis[x+1]) { vis[x+1]=1;que.push(make_node(x+1,now.step+1)); } if(judge(x-1)&&!vis[x-1]) { vis[x-1]=1;que.push(make_node(x-1,now.step+1)); } if(judge(2*x)&&!vis[x*2]) { vis[x*2]=1;que.push(make_node(2*x,now.step+1)); } } printf("%d ",ans); } }