POJ 3252 round numbers(数位DP）

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <cmath>
#include <vector>
#include <queue>
#include <cstring>
#include <set>
#include <stack>
#include <map>
#define LL long long
using namespace std;
int dp[50][50][50];
int bit[40];
int dfs(int pos,int num0,int num1,bool flag,bool first)
{
	if(pos == 0) return num0 >= num1;
	if(!flag && dp[pos][num0][num1] != -1)
		return dp[pos][num0][num1];
	int ans = 0;
	int end = flag ? bit[pos] : 1;
	for(int i=0;i<=end;i++)
	{
		ans += dfs(pos-1, (first && i == 0) ? 0 : num0 + (i==0),  (first && i == 0) ? 0 : num1 + (i == 1),  flag &&(i == end), first && (i == 0));
	}
	if(!flag) dp[pos][num0][num1] = ans;
	return ans;
}
int solve(int n)
{
	int len = 0;
	memset(bit,0,sizeof(bit));
	while(n)
	{
		bit[++len] = n & 1;
		n >>= 1;
	}
	return dfs(len,0,0,1,1);
}
int main()
{
	int l, r;
	while(scanf("%d%d", &l, &r)!=EOF)
	{
		memset(dp, -1, sizeof(dp));
		printf("%d\n", solve(r) - solve(l-1));
	}
	return 0;
}