solution for 2.7 O(n)

Author: amejiarosario

src/linked-list/intersection.js

@@ -21,8 +21,14 @@ function intersectionBad(list1, list2) {
 
   return intersection;
 }
-
-function intersection(list1, list2) {
+/**
+ *  O(m * n)
+ *
+ * @param list1
+ * @param list2
+ * @returns {*}
+ */
+function intersection2(list1, list2) {
   let intersection = null;
 
   for(let i1 = list1.head; i1; i1 = i1.next) {
@@ -36,4 +42,38 @@ function intersection(list1, list2) {
   return intersection;
 }
 
+// O(m + n) : using Hash of reference (not value)
+
+/**
+ * If there's an intersection both ends are the same.
+ *
+ * O(n)
+ *
+ * @param list1
+ * @param list2
+ */
+function intersection(list1, list2) {
+  if(list1.tail !== list2.tail) {
+    return null;
+  }
+
+  let i1 = list1.head;
+  let i2 = list2.head;
+
+  if(list1.size() > list2.size()) {
+    for(let i = 0; i < list1.size() - list2.size(); i++) { i1 = i1.next; }
+  }
+
+  if(list2.size() > list1.size()) {
+    for(let i = 0; i < list2.size() - list1.size(); i++) { i2 = i2.next; }
+  }
+
+  while(i1 && i2 && i1 !== i2) {
+    i1 = i1.next;
+    i2 = i2.next;
+  }
+
+  return i1;
+}
+
 module.exports = intersection;