Codeforces Round #320 (Div. 2) "Or" Game(好题,贪心/位运算/前缀后缀或)

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<algorithm>
 4 #include<iostream>
 5 using namespace std;
 6 typedef long long ll;
 7 /*
 8 n个数,你最多有k次操作,每次操作可以选择一个数乘以x,问所有数或(|)的最大值 
 9 贪心思路:选一个数进行k此乘以x操作; 因为x>=2 
10             111        --->   1111
11             111     --->   1111
12             不如  
13             111        --->    11111;
14             111        --->    111; 
15 用到了前缀和后缀的思想 :
16 */
17 ll pre[200005];　　　　// pre[i]是 a[1]|a[2].....|a[i];
18 ll suf[200005];
19 ll a[200005];
20 ll ans; 
21 int main(){
22     
23     int n,k,x;
24     while(scanf("%d%d%d",&n,&k,&x) != EOF){
25         for(int i = 1 ; i <= n ; i ++)    scanf("%I64d",&a[i]);
26         for(int i = 1 ; i <= n ; i ++) pre[i] = pre[i-1]|a[i];
27         for(int i = n ; i >= 1 ; i --) suf[i] = suf[i+1]|a[i];
28         ll num = 1;
29         for(int i = 1 ; i <= k ; i ++) num *= x;
30         for(int i = 1 ; i <= n ; i ++) ans = max(ans,pre[i-1]|a[i]*num|suf[i+1]);
31         printf("%I64d\n",ans);
32     }
33     
34     
35     return 0;
36 }