Merge pull request #2693 from aadil42/patch-69

Author: aakhtar3

javascript/2130-maximum-twin-sum-of-a-linked-list.js

@@ -0,0 +1,62 @@
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val, next) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.next = (next===undefined ? null : next)
+ * }
+ */
+
+/**
+ * Linear Time 
+ * Time O(n) | Space O(1)
+ * @param {ListNode} head
+ * @return {number}
+ */
+var pairSum = function (head) {
+  const mid = llLength(head) / 2;
+  const rightPointer = getRightPointer(head, mid);
+  const leftPointer = reverseLL(head, mid);
+  
+  return getMax(leftPointer, rightPointer);
+};
+
+var getMax = (leftPointer, rightPointer) => {
+    let max = 0;
+    while (leftPointer && rightPointer) {
+      max = Math.max(leftPointer.val + rightPointer.val, max);
+      leftPointer = leftPointer.next;
+      rightPointer = rightPointer.next;
+    }
+    return max;
+}
+var getRightPointer = (head, mid) => {
+    let count = 0;
+    let rightPointer = head;
+    while (count < mid) {
+    rightPointer = rightPointer.next;
+      count++;
+    }
+    return rightPointer;
+}
+
+var llLength = (head) => {
+  let count = 0;
+  while (head) {
+    head = head.next;
+    count++;
+  }
+  return count;
+};
+
+var reverseLL = (head, len) => {
+  let count = 0;
+  let temp = null;
+  while (count < len) {
+    const next = head.next;
+    head.next = temp;
+    temp = head;
+    head = next;
+    count++;
+  }
+  return temp;
+};