Add Solution to day 2

05- May/02- Sign of the Product of an Array/02- Sign of the Product of an Array (Ahmed Gamal).js

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+// Author: Ahmed Gamal
+
+// for this problem, we just need to keep track of two important things that determine the sign of the product of the array:
+// 1- if the array contains a zero, then the product will be zero (regardless of the other values in the array)
+// 2- if the array contains an odd number of negative values, then the product will be negative, otherwise it will be positive
+
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var arraySign = function(nums) {
+    // odd: true if the number of negative values is odd, false otherwise
+    // zero: true if the array contains a zero, false otherwise
+    let odd = false, zero = false;
+
+    // loop through the array and update the values of odd and zero
+    nums.forEach(x => {
+        // if x < 0, then odd will be true if it was false, and false if it was true (using XOR)
+        odd ^= x < 0;
+
+        // if x === 0, then zero will be true
+        zero |= x === 0;
+    });
+
+    // if zero is true, then the product will be zero regardless of the value of odd
+    if(zero) {
+        return 0;
+    }
+
+    // if odd is true, then the product will be negative, otherwise it will be positive
+    return (odd && -1) || 1;
+};