LeetCode 1310. 子数组异或查询（前缀异或）

示例 1：
输入：arr = [1,3,4,8], queries = [[0,1],[1,2],[0,3],[3,3]]
输出：[2,7,14,8] 
解释：
数组中元素的二进制表示形式是：
1 = 0001 
3 = 0011 
4 = 0100 
8 = 1000 
查询的 XOR 值为：
[0,1] = 1 xor 3 = 2 
[1,2] = 3 xor 4 = 7 
[0,3] = 1 xor 3 xor 4 xor 8 = 14 
[3,3] = 8

示例 2：
输入：arr = [4,8,2,10], queries = [[2,3],[1,3],[0,0],[0,3]]
输出：[8,0,4,4]
 
提示：
1 <= arr.length <= 3 * 10^4
1 <= arr[i] <= 10^9
1 <= queries.length <= 3 * 10^4
queries[i].length == 2
0 <= queries[i][0] <= queries[i][1] < arr.length

class Solution {
public:
    vector<int> xorQueries(vector<int>& arr, vector<vector<int>>& queries) {
    	int i, j=0, l, r;
    	for(i = 1; i < arr.size(); ++i)
    		arr[i] ^= arr[i-1];
    	vector<int> ans(queries.size());
    	for(i = 0; i < queries.size(); ++i)
    	{
    		l = queries[i][0];
    		r = queries[i][1];
    		ans[j++] = (l > 0 ? arr[r]^arr[l-1] : arr[r]);
    	}
    	return ans;
    }
};