solve 160.intersection-of-two-linked-lists

Author: andavid

vscode/160.intersection-of-two-linked-lists.java

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+/*
+ * @lc app=leetcode id=160 lang=java
+ *
+ * [160] Intersection of Two Linked Lists
+ *
+ * https://leetcode.com/problems/intersection-of-two-linked-lists/description/
+ *
+ * algorithms
+ * Easy (35.22%)
+ * Likes:    2346
+ * Dislikes: 228
+ * Total Accepted:    334.3K
+ * Total Submissions: 949.2K
+ * Testcase Example:  '8\n[4,1,8,4,5]\n[5,0,1,8,4,5]\n2\n3'
+ *
+ * Write a program to find the node at which the intersection of two singly
+ * linked lists begins.
+ *
+ * For example, the following two linked lists:
+ *
+ *
+ * begin to intersect at node c1.
+ *
+ *
+ *
+ * Example 1:
+ *
+ *
+ *
+ * Input: intersectVal = 8, listA = [4,1,8,4,5], listB = [5,0,1,8,4,5], skipA =
+ * 2, skipB = 3
+ * Output: Reference of the node with value = 8
+ * Input Explanation: The intersected node's value is 8 (note that this must
+ * not be 0 if the two lists intersect). From the head of A, it reads as
+ * [4,1,8,4,5]. From the head of B, it reads as [5,0,1,8,4,5]. There are 2
+ * nodes before the intersected node in A; There are 3 nodes before the
+ * intersected node in B.
+ *
+ *
+ *
+ * Example 2:
+ *
+ *
+ *
+ * Input: intersectVal = 2, listA = [0,9,1,2,4], listB = [3,2,4], skipA = 3,
+ * skipB = 1
+ * Output: Reference of the node with value = 2
+ * Input Explanation: The intersected node's value is 2 (note that this must
+ * not be 0 if the two lists intersect). From the head of A, it reads as
+ * [0,9,1,2,4]. From the head of B, it reads as [3,2,4]. There are 3 nodes
+ * before the intersected node in A; There are 1 node before the intersected
+ * node in B.
+ *
+ *
+ *
+ *
+ * Example 3:
+ *
+ *
+ *
+ * Input: intersectVal = 0, listA = [2,6,4], listB = [1,5], skipA = 3, skipB =
+ * 2
+ * Output: null
+ * Input Explanation: From the head of A, it reads as [2,6,4]. From the head of
+ * B, it reads as [1,5]. Since the two lists do not intersect, intersectVal
+ * must be 0, while skipA and skipB can be arbitrary values.
+ * Explanation: The two lists do not intersect, so return null.
+ *
+ *
+ *
+ *
+ * Notes:
+ *
+ *
+ * If the two linked lists have no intersection at all, return null.
+ * The linked lists must retain their original structure after the function
+ * returns.
+ * You may assume there are no cycles anywhere in the entire linked
+ * structure.
+ * Your code should preferably run in O(n) time and use only O(1) memory.
+ *
+ *
+ */
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) {
+ *         val = x;
+ *         next = null;
+ *     }
+ * }
+ */
+public class Solution {
+  public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
+    int lenA = 0;
+    ListNode pA = headA;
+    for (; pA != null; pA = pA.next) {
+      lenA++;
+    }
+
+    int lenB = 0;
+    ListNode pB = headB;
+    for (; pB != null; pB = pB.next) {
+      lenB++;
+    }
+
+    if (pA != pB) {
+      return null;
+    }
+
+    pA = headA;
+    pB = headB;
+    int len = lenA - lenB;
+    if (lenA < lenB) {
+      pA = headB;
+      pB = headA;
+      len = lenB - lenA;
+    }
+
+    while (len > 0) {
+      pA = pA.next;
+      len--;
+    }
+
+    while (pA != null && pB != null) {
+      if (pA == pB) {
+        return pA;
+      } else {
+        pA = pA.next;
+        pB = pB.next;
+      }
+    }
+
+    return null;
+  }
+}
+