constructArr.js

Author: amit265

javascript/4_array-programs/constructArr.js

@@ -0,0 +1,28 @@
+// 42. Construct an Array from its pair-sum Array
+
+function constructArr(pair, n) {
+  let arr = new Array(n);
+
+  arr[0] = Math.floor((pair[0] + pair[1] - pair[n - 1]) / 2);
+  for (let i = 1; i < n; i++) {
+    arr[i] = pair[i - 1] - arr[0];
+  }
+
+  return arr;
+}
+
+function calculateOriginalArrayLength(pairSumArrayLength) {
+  return Math.ceil(Math.sqrt(8 * pairSumArrayLength + 1) + 1) / 2;
+}
+
+let pair = [13, 11, 10, 13, 10, 9, 12, 7, 10, 9];
+
+const arrayLength = pair.length;
+
+const originalArrayLength = calculateOriginalArrayLength(arrayLength);
+
+let n = originalArrayLength;
+
+let orginalArr = constructArr(pair, n);
+
+console.log("Original Arr", orginalArr);