Codeforces Round #267 (Div. 2) B. Fedor and New Game【位运算/给你m+1个数让你判断所给数的二进制形式与第m+1个数不相同的位数是不是小于等于k,是的话就累计起来】
After you had helped George and Alex to move in the dorm, they went to help their friend Fedor play a new computer game «Call of Soldiers 3».
The game has (m + 1) players and n types of soldiers in total. Players «Call of Soldiers 3» are numbered form 1 to (m + 1). Types of soldiers are numbered from 0 to n - 1. Each player has an army. Army of the i-th player can be described by non-negative integer xi. Consider binary representation of xi: if the j-th bit of number xi equal to one, then the army of the i-th player has soldiers of the j-th type.
Fedor is the (m + 1)-th player of the game. He assume that two players can become friends if their armies differ in at most k types of soldiers (in other words, binary representations of the corresponding numbers differ in at most k bits). Help Fedor and count how many players can become his friends.
The first line contains three integers n, m, k (1 ≤ k ≤ n ≤ 20; 1 ≤ m ≤ 1000).
The i-th of the next (m + 1) lines contains a single integer xi (1 ≤ xi ≤ 2n - 1), that describes the i-th player's army. We remind you that Fedor is the (m + 1)-th player.
Print a single integer — the number of Fedor's potential friends.
7 3 1 8 5 111 17
0
3 3 3 1 2 3 4
3
【分析】:
“<< ” 位左移,相当于乘以2 “>>" 位右移,相当于除以2 “&” 按为与,位数都为1时为1,否则为0 “^” 异或,不同为1,相同为0 新技能: a & (1 << j ) 表示数a二进制的第j位是什么
【代码】:
#include <bits/stdc++.h> using namespace std; const int maxn = 1005; int n,m,k,a[maxn]; int main() { int sum=0,ans=0; cin>>n>>m>>k; for(int i=0;i<=m;i++) cin>>a[i]; for(int i=0;i<m;i++) { sum=0; //注意内部清零 for(int j=0;j<n;j++) if( ( a[i]&(1<<j) )^( a[m]&(1<<j) ) ) sum++; if(sum<=k) ans++; } cout<<ans<<endl; return 0; }