poj 3252 Round Numbers 数位dp

题目链接

找一个范围内二进制中0的个数大于等于1的个数的数的数量。基础的数位dp

#include<bits/stdc++.h>
using namespace std;
#define mem1(a) memset(a, -1, sizeof(a))
int digit[50], dp[50][50][50], len;
int dfs(int len, int num0, int num1, int f, int first) {        //first记录前面是否全部为0
    if(!len) {
        return num0>=num1;
    }
    if(!f&&!first&&dp[len][num0][num1]!=-1)
        return dp[len][num0][num1];
    int ret = 0, maxx = f?digit[len]:1;
    for(int i = 0; i<=maxx; i++) {
        if(i == 0) {
            ret += dfs(len-1, first?0:num0+1, num1, f&&i==maxx, first);
        } else {
            ret += dfs(len-1, num0, num1+1, f&&i==maxx, 0);
        }
    }
    if(!f&&!first)
        return dp[len][num0][num1] = ret;
    return ret;
}
int cal(int n) {
    len = 0;
    while(n) {
        digit[++len] = n&1;
        n>>=1;
    }
    return dfs(len, 0, 0, 1, 1);
}
int main()
{
    int a, b;
    mem1(dp);
    while(~scanf("%d%d", &a, &b)) {
        printf("%d
", cal(b)-cal(a-1));
    }
}