Codeforces484a--bits (greedy algorithm)

Bits

Let's denote as the number of bits set (' 1 ' bits) in the binary representation of the non-negative integer x.
You are given multiple queries consisting of pairs of integers l and R. For each query, find the X, such this l≤x≤r, and is maximum possible. If There is multiple such numbers find the smallest of them.
Input
The first line contains integer n-the number of Queries (1≤n≤10000).
Each of the following n lines contain and integers li, ri-the arguments for the corresponding query (0≤li≤ri≤1018) .
Output
For each query, print the answer in a separate line.
Sample Test (s)
Input
3
1 2
2 4
1 10
Output
1
3
7
Main topic:

Given l,r, the output x,x is the number that is the most numerous after the binary in [L,r], (there are multiple solutions at the same time, the output is the smallest one).

Problem Solving Ideas:

The l,r has the same T1 bit from the high position, so according to Common sense, the first T1 bit of x (starting from high) must also be the same as LR. And because L<=r, then t1+1 bit different, must be L for 0,r for 1.

At this point, the t1+1 bit of x is assigned a value of 0, followed by all 1. Then the X:L<=X<R is established and the optimal solution is obtained in the [L,r] interval.

There is a special case: R is converted to binary after all is 1, so add a judgment. Determine if x is absolutely greater than r when the t1+1 bit is 1, and is definitely greater than the t1+1 assignment to 0, whereas the value is 1.

Code:

1 /*************************************************************************2 > File Name:CF484A.cpp3 > Author:enumz4 > Mail: [email protected]5 > Created time:2014 November 06 Thursday 01:49 25 seconds6  ************************************************************************/7 8#include <iostream>9#include <cstdio>Ten#include <cstdlib> One#include <string> A#include <cstring> -#include <list> -#include <queue> the#include <stack> -#include <map> -#include <Set> -#include <algorithm> +#include <cmath> -#include <bitset> +#include <climits> A #defineMAXN 100000 at #defineLL Long Long - using namespacestd; - intMain () - { - LL A,b,ans; -     intt,k; inCin>>T; -      while(t--) to     { +ans=0; -Cin>>a>>b; the         inti; *         BOOLflag=0; $          for(i= -; i>=0; i--)Panax Notoginseng         { -             if(flag) the             { +ans+=1ll<<i; A                 Continue; the             } +             if((a& (1ll<<i)) = = (b& (1ll<<i))) -             { $                 if((a& (1ll<<i))! =0) $ans+=1ll<<i; -             } -             Else the             { -flag=1;Wuyik=i; thei++; -             } Wu         } -         if(ans>b) Aboutans=ans^ (1ll<<k); $cout<<ans<<Endl; -     } -     return 0; -}

Codeforces484a--bits (greedy algorithm)