Create 1664-ways-to-make-a-fair-array.js

Author: everthis

1664-ways-to-make-a-fair-array.js

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+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+const waysToMakeFair = function (nums) {
+  const n = nums.length
+  const preOddSum = new Array(n + 1).fill(0)
+  const preEvenSum = new Array(n + 1).fill(0)
+  for (let i = 0; i < n; i++) {
+    if (i % 2 === 0) {
+      preEvenSum[i + 1] = nums[i] + preEvenSum[i]
+      preOddSum[i + 1] = preOddSum[i]
+    } else {
+      preOddSum[i + 1] = nums[i] + preOddSum[i]
+      preEvenSum[i + 1] = preEvenSum[i]
+    }
+  }
+  let ret = 0
+  for (let i = 0; i < n; i++) {
+    if (
+      preEvenSum[i] + preOddSum[n] - preOddSum[i + 1] ===
+      preOddSum[i] + preEvenSum[n] - preEvenSum[i + 1]
+    )
+      ret++
+  }
+  return ret
+}