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[], dp[][][], 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]!=-)
         return dp[len][num0][num1];
     int ret = , maxx = f?digit[len]:;
     for(int i = ; i<=maxx; i++) {
         if(i == ) {
             ret += dfs(len-, first?:num0+, num1, f&&i==maxx, first);
         } else {
             ret += dfs(len-, num0, num1+, f&&i==maxx, );
         }
     }
     if(!f&&!first)
         return dp[len][num0][num1] = ret;
     return ret;
 }
 int cal(int n) {
     len = ;
     while(n) {
         digit[++len] = n&;
         n>>=;
     }
     return dfs(len, , , , );
 }
 int main()
 {
     int a, b;
     mem1(dp);
     while(~scanf("%d%d", &a, &b)) {
         printf("%d\n", cal(b)-cal(a-));
     }
 }