（14）CountTriplets

一、问题描述

给定一个数组。三个索引

• i，i ~ [0, array.length)
• j,  j ~ [0, array.length)
• k, k ~ [0, array.length)

求有多少种组合方式使得 array[i] & array[j] & array[k] = 0?

二、思路

用缓存存储遍历过的结果

三、Code

 package algorithm;

 import java.util.Arrays;

 /**
  * Created by adrian.wu on 2019/2/27.
  */
 public class CountTriplets {
     public int countTriplets(int[] A) {
         int n = A.length, res = 0;
         int[] vd = new int[(1 << 16)];
         Arrays.fill(vd, -1);
         for (int i = 0; i < n; i++) {
             for (int j = 0; j < n; j++) {
                 int ijAnd = A[i] & A[j];
                 if (vd[ijAnd] == -1) {
                     vd[ijAnd] = 0;
                     for (int k = 0; k < n; k++) {
                         if ((ijAnd & A[k]) == 0) vd[ijAnd]++;
                     }
                 }
                 res += vd[ijAnd];
             }
         }
         return res;
     }
 }