1442. Count Triplets That Can Form Two Arrays of Equal XOR - Medium - Leetcode - 解題筆記 | Hsing Yu = = We are the dreamers. We make it happen 'cause we can see it.

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# 題目敘述

Given an array of integers arr .

We want to select three indices i , j and k where (0 <= i < j <= k < arr.length) .

Let's define a and b as follows:

a = arr[i] ^ arr[i + 1] ^ ... ^ arr[j - 1]
b = arr[j] ^ arr[j + 1] ^ ... ^ arr[k]
Note that ^ denotes the bitwise-xor operation.

Return the number of triplets ( i , j and k ) Where a == b .

Input: arr = [2,3,1,6,7]
Output: 4
Explanation: The triplets are (0,1,2), (0,2,2), (2,3,4) and (2,4,4)

Input: arr = [1,1,1,1,1]
Output: 10

Solution.java

	class Solution {
	public int countTriplets(int[] arr) {
	int[] prefix = new int[arr.length + 1];

	for (int i = 0; i < arr.length; i++) {
	prefix[i + 1] = prefix[i] ^ arr[i];
	}

	int count = 0;

	for (int i = 0; i < arr.length; i++) {
	for (int k = i + 1; k < arr.length; k++) {
	if (prefix[i] == prefix[k + 1]) {
	count += k - i;
	}
	}
	}

	return count;
	}
	}

Solution.java

	class Solution {
	public int countTriplets(int[] arr) {
	int count = 0;

	for (int i = 0; i < arr.length; i++) {
	int curr_XOR = 0;
	for (int k = i; k < arr.length; k++) {
	curr_XOR ^= arr[k];
	if(curr_XOR == 0) count += k - i;
	}
	}

	return count;
	}
	}

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