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Round Numbers
Description The cows, as you know, have no fingers or thumbs and thus are unable to play Scissors, Paper, Stone‘ (also known as ‘Rock, Paper, Scissors‘, ‘Ro, Sham, Bo‘, and a host of other names) in order to make arbitrary decisions such as who gets to be milked first. They have thus resorted to "round number" matching. The first cow picks an integer less than two billion. The second cow does the same. If the numbers are both "round numbers", the first cow wins, otherwise the second cow wins. A positive integer N is said to be a "round number" if the binary representation of N has as many or more zeroes than it has ones. For example, the integer 9, when written in binary form, is 1001. 1001 has two zeroes and two ones; thus, Obviously, it takes cows a while to convert numbers to binary, so the winner takes a while to determine. Bessie wants to cheat and thinks she can do that if she knows how many "round numbers" are in a given range. Help her by writing a program that tells how many round numbers appear in the inclusive range given by the input (1 ≤ Start <Finish ≤ 2,000,000,000). Input Line 1: Two space-separated integers, respectively Start and Finish. Output Line 1: A single integer that is the count of round numbers in the inclusive range Start..Finish Sample Input 2 12 Sample Output 6 Source |
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转化成二进制然后按位dp统计0和1的个数
注意判断是否是前导0
ACcode：
#include <cstdio>
#include <iostream>
#include <cstring>
using namespace std;
int dp[40][40][40];
int a,b;
int data[40];
int dfs(int len,int is_0,int is_1,int pre,int limit){
if(!len)return is_0>=is_1;
if(!pre&&!limit&&dp[len][is_0][is_1]!=-1)return dp[len][is_0][is_1];
int ed=limit?data[len]:1;
int ans=0;
for(int i=0;i<=ed;++i){
if(pre){
if(i==0)ans+=dfs(len-1,0,0,1,limit&&i==ed);
else ans+=dfs(len-1,is_0,is_1+1,0,limit&&i==ed);
}
else {
if(i==0)ans+=dfs(len-1,is_0+1,is_1,0,limit&&i==ed);
else ans+=dfs(len-1,is_0,is_1+1,0,limit&&i==ed);
}
}
if(!limit&&!pre)dp[len][is_0][is_1]=ans;
return ans;
}
int fun(int a){
int len=0;
while(a){
data[++len]=a%2;
a>>=1;
}
return dfs(len,0,0,1,1);
}
void doit(){
printf("%d\n",fun(b)-fun(a-1));
}
int main(){
memset(dp,-1,sizeof(dp));
while(~scanf("%d%d",&a,&b))doit();
return 0;
}