feat: 2588. Count the Number of Beautiful Subarrays, 前缀和+hash

Author: upupming

leetcode/残酷刷题/2588. Count the Number of Beautiful Subarrays.js

@@ -0,0 +1,20 @@
+/**
+ * @param {number[]} nums
+ * @return {number}
+
+3, 1, 2 => 11, 01, 10
+4, 3, 1, 2, 4 => 100, 11, 01, 10, 100
+满足条件的子数组：每一位上 1 出现的次数为偶数次，异或结果为 0
+异或结果 <= 10^6，因此可以存储下 map[异或结果] = 前面的出现次数
+ */
+var beautifulSubarrays = function(nums) {
+  let mp = {}, n = nums.length, xor = 0, ans = 0
+  mp[0] = 1
+  for (let i = 0; i < n; i++) {
+      xor ^= nums[i]
+      ans += mp[xor] ?? 0
+      mp[xor] ??= 0
+      mp[xor]++
+  }
+  return ans
+};