Solution for problem 1664 (fishercoder1534#139)

* Add solution for problem 1664

* Add js file

Author: ltp88

README.md

@@ -8,6 +8,7 @@ _If you like this project, please leave me a star._ ★
 
 |  #  |      Title     |   Solutions   | Video  | Difficulty  | Tag                   
 |-----|----------------|---------------|--------|-------------|-------------
+|1664|[Ways to Make a Fair Array](https://leetcode.com/problems/ways-to-make-a-fair-array/)|[Javascript](./javascript/_1664.js) ||Medium|Greedy|
 |1663|[Smallest String With A Given Numeric Value](https://leetcode.com/problems/smallest-string-with-a-given-numeric-value/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1663.java) ||Medium|Greedy|
 |1662|[Check If Two String Arrays are Equivalent](https://leetcode.com/problems/check-if-two-string-arrays-are-equivalent/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1662.java) ||Easy|String|
 |1658|[Minimum Operations to Reduce X to Zero](https://leetcode.com/problems/minimum-operations-to-reduce-x-to-zero/)|[Javascript](./javascript/_1658.js)||Medium|Greedy|

javascript/_1664.js

@@ -0,0 +1,37 @@
+// Author: Phuong Lam
+
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var waysToMakeFair = function (nums) {
+  var total = 0
+
+  var lo = 0 // left odd
+  var le = 0 // left even
+  var ro = 0 // right odd
+  var re = 0 // right even
+
+  // when ignore 1 element => right odd mean i % 2 === 0
+  for (i = 0; i < nums.length; i++) {
+    if (i % 2 === 0) ro += nums[i]
+    else re += nums[i]
+  }
+
+  // remove position i, recalculate left - right even-odd
+  for (i = 0; i < nums.length; i++) {
+    // recalculate left
+    if (i > 0) {
+      if (i % 2 === 0) lo += nums[i - 1]
+      else le += nums[i - 1]
+    }
+
+    // recalculate right
+    if (i % 2 === 0) ro -= nums[i]
+    else re -= nums[i]
+
+    // calc total even & odd
+    if (lo + ro === le + re) total++
+  }
+  return total
+}