1664. 生成平衡数组的方案数

Author: w2xi

README.md

@@ -190,6 +190,7 @@
 |1002|[查找共用字符](https://leetcode.cn/problems/find-common-characters/)|[JavaScript](./algorithms/find-common-characters.js)|Easy|
 |1038|[从二叉搜索树到更大和树](https://leetcode.cn/problems/binary-search-tree-to-greater-sum-tree/)|[JavaScript](./algorithms/binary-search-tree-to-greater-sum-tree.js)|Medium|
 |1047|[删除字符串中的所有相邻重复项](https://leetcode.cn/problems/remove-all-adjacent-duplicates-in-string/)|[JavaScript](./algorithms/remove-all-adjacent-duplicates-in-string.js)|Easy|
+|1664|[生成平衡数组的方案数](https://leetcode.cn/problems/ways-to-make-a-fair-array/)|[JavaScript](./algorithms/ways-to-make-a-fair-array.js)|Medium|
 |1780|[判断一个数字是否可以表示成三的幂的和](https://leetcode.cn/problems/check-if-number-is-a-sum-of-powers-of-three/)|[JavaScript](./algorithms/check-if-number-is-a-sum-of-powers-of-three.js)|Medium|
 |1807|[替换字符串中的括号内容](https://leetcode.cn/problems/evaluate-the-bracket-pairs-of-a-string/)|[JavaScript](./algorithms/evaluate-the-bracket-pairs-of-a-string.js)|Medium|
 |1813|[句子相似性 III](https://leetcode.cn/problems/sentence-similarity-iii/)|[JavaScript](./algorithms/sentence-similarity-iii.js)|Medium|

algorithms/ways-to-make-a-fair-array.js

@@ -0,0 +1,44 @@
+/**
+ * 1664. 生成平衡数组的方案数
+ * @param {number[]} nums
+ * @return {number}
+ */
+var waysToMakeFair = function (nums) {
+  /**
+   * [2, 1, 6, 4]
+   * even: 8; odd: 5
+   * | index | even  | odd |   8  |  5  | 
+   * |   0   | 1+4=5 |  6  |   6  |  5  |
+   * |   1   | 2+4+6 |  6  |   6  |  4  |
+   * |   2   | 2+4=6 |  1  |   0  |  4  |
+   * |   3   | 2+6=8 |  1  |   0  |  1  |
+   * 总体思路: 前缀后缀`奇偶`和
+   */
+  let odd1 = 0, even1 = 0; // 后缀和
+  for (let i = 0; i < nums.length; i++) {
+    if (i % 2 === 0) {
+      even1 += nums[i];
+    } else {
+      odd1 += nums[i];
+    }
+  }
+  let odd2 = 0, even2 = 0; // 前缀和
+  let count = 0;
+  for (let i = 0; i < nums.length; i++) {
+    if (i % 2 === 0) {
+      even1 -= nums[i];
+    } else {
+      odd1 -= nums[i];
+    }
+    if (odd1 + even2 === even1 + odd2) {
+      count++;
+    }
+    if (i % 2 === 0) {
+      even2 += nums[i];
+    } else {
+      odd2 += nums[i];
+    }
+  }
+
+  return count;
+};

vs-lt/1664.生成平衡数组的方案数.js

@@ -0,0 +1,52 @@
+/*
+ * @lc app=leetcode.cn id=1664 lang=javascript
+ *
+ * [1664] 生成平衡数组的方案数
+ */
+
+// @lc code=start
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var waysToMakeFair = function(nums) {
+  /**
+   * [2, 1, 6, 4]
+   * even: 8; odd: 5
+   * | index | even  | odd |   8  |  5  | 
+   * |   0   | 1+4=5 |  6  |   6  |  5  |
+   * |   1   | 2+4+6 |  6  |   6  |  4  |
+   * |   2   | 2+4=6 |  1  |   0  |  4  |
+   * |   3   | 2+6=8 |  1  |   0  |  1  |
+   * 总体思路: 前缀后缀`奇偶`和
+   */
+  let odd1 = 0, even1 = 0; // 后缀和
+  for (let i = 0; i < nums.length; i++) {
+    if (i % 2 === 0) {
+      even1 += nums[i];
+    } else {
+      odd1 += nums[i];
+    }
+  }
+  let odd2 = 0, even2 = 0; // 前缀和
+  let count = 0;
+  for (let i = 0; i < nums.length; i++) {
+    if (i % 2 === 0) {
+      even1 -= nums[i];
+    } else {
+      odd1 -= nums[i];
+    }
+    if (odd1 + even2 === even1 + odd2) {
+      count++;
+    }
+    if (i % 2 === 0) {
+      even2 += nums[i];
+    } else {
+      odd2 += nums[i];
+    }
+  }
+
+  return count;
+};
+// @lc code=end
+