LinkList 2

Problem1

@@ -0,0 +1,51 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode() {}
+ *     TreeNode(int val) { this.val = val; }
+ *     TreeNode(int val, TreeNode left, TreeNode right) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+ //TC On
+ //SC On
+class BSTIterator {
+    TreeNode root;
+    Queue<Integer> q = new LinkedList();
+
+    public BSTIterator(TreeNode root) {
+        this.root = root;
+        helper(root);
+
+    }
+
+    public int next() {
+        return q.poll();
+    }
+
+    public boolean hasNext() {
+        return !q.isEmpty();
+    }
+
+    private void helper(TreeNode root) {
+        if (root == null)
+            return ;
+        helper(root.left);
+        q.add(root.val);
+        helper(root.right);
+
+    }
+}
+
+/**
+ * Your BSTIterator object will be instantiated and called as such:
+ * BSTIterator obj = new BSTIterator(root);
+ * int param_1 = obj.next();
+ * boolean param_2 = obj.hasNext();
+ */

Problem2

@@ -0,0 +1,57 @@
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode() {}
+ *     ListNode(int val) { this.val = val; }
+ *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
+ * }
+ */
+ //TC On SC O1
+class Solution {
+    public void reorderList(ListNode head) {
+        ListNode slow = head;
+        ListNode fast = head;
+        //find mid
+        ListNode mid = mid(head);
+        // rev
+        ListNode revHead = revList(mid.next);
+        //map
+        mid.next=null;
+        fast=revHead;
+        while(fast!=null){
+        ListNode temp=slow.next;
+        slow.next=fast;
+        fast=fast.next;
+        slow.next.next=temp;
+        slow=temp;
+
+        }
+
+    }
+
+    private ListNode mid(ListNode head) {
+        ListNode slow = head;
+        ListNode fast = head;
+        while (fast != null && fast.next != null) {
+            slow = slow.next;
+            fast = fast.next.next;
+        }
+        return slow;
+
+    }
+
+    private ListNode revList(ListNode head) {
+        ListNode curr = head;
+        ListNode prev = null;
+        while (curr != null) {
+            ListNode temp = curr.next;
+            curr.next = prev;
+            prev = curr;
+            curr = temp;
+        }
+        return prev;
+
+    }
+}

Problem3

@@ -0,0 +1,25 @@
+//tc On
+//sc o1
+
+/*
+class Node
+{
+    int data ;
+    Node next;
+    Node(int d)
+    {
+        data = d;
+        next = null;
+    }
+}
+*/
+
+class Solution {
+    public void deleteNode(Node del_node) {
+        // code here
+        Node temp=del_node.next;
+        del_node.data=temp.data;
+        del_node.next=temp.next;
+        temp=null;
+    }
+}

Problem4

@@ -0,0 +1,65 @@
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) {
+ *         val = x;
+ *         next = null;
+ *     }
+ * }
+ */
+// TC O(m+n)
+SC O(1)
+public class Solution {
+    public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
+
+        if (headA == headB) {
+            return headA;
+        }
+
+        int countA = 0;
+        int countB = 0;
+        int skipSteps = -1;
+        boolean isAbig = false;
+        ListNode tempA=headA;
+
+        ListNode tempB=headB;
+        while (headA.next != null) {
+            headA=headA.next;
+            countA++;
+
+        }
+        while (headB.next != null) {
+              headB=headB.next;
+            countB++;
+        }
+        if (countA > countB) {
+            skipSteps = countA - countB;
+            isAbig = true;
+        }
+        if (countB > countA) {
+            skipSteps = countB - countA;
+        }
+          headA=tempA;
+          headB=tempB;
+
+        if (isAbig && skipSteps != -1) {
+           for(int i=0;i<skipSteps;i++){
+            headA=headA.next;
+           }}
+           else if(!isAbig && skipSteps != -1){
+            for(int i=0;i<skipSteps;i++){
+            headB=headB.next;
+           }
+        }
+
+        while(headA!=null){
+            if(headA==headB) return headA;
+            headA=headA.next;
+            headB=headB.next;
+        }
+
+        return headA;
+    }
+}