POJ3252 Round Numbers 数位DP

#include <cstdio>
#include <string>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <vector>
#define maxn 30
using namespace std;
#define ll long long
int limit[40],dp[40][40][40];
int dfs(int now,int prev,int have,int first,bool flag)
{//prev存储0的个数，have存储1的个数，first存储此时是否含有前导0
    if(now<=0)
    {
        if(first) return prev>=have;
        else return 0;
    }
    if(!flag&&dp[now][prev][have]!=-1&&first) return dp[now][prev][have];
    int bound=flag?limit[now]:1,ret=0;
    for(int k=0;k<=bound;k++)
    {
        if(first)
        {
            ret+=dfs(now-1,prev+!k,have+k,first,flag&&(k==bound));
        }
        else
        {
            if(k==0)
            ret+=dfs(now-1,0,0,0,flag&&(k==bound));
            else
            ret+=dfs(now-1,0,1,1,flag&&(k==bound));
        }
    }
    if(!flag) dp[now][prev][have]=ret;
    return ret;
}
int count(int x)
{
    int len=0;
    while(x)//使用位运算得到x中每位的值
    {
        limit[++len]=x&1;
        x>>=1;
    }
    return dfs(len,0,0,0,true);
}
int main()
{
    int n,m;
    memset(dp,-1,sizeof(dp));
    while(cin>>n>>m)
    {
        cout<<count(m)-count(n-1)<<endl;
    }
    return 0;
}