added more question

Author: rajat.gupta

reorder_list.java

@@ -0,0 +1,72 @@
+package leetcode;
+//https://leetcode.com/problems/reorder-list/
+public class reorder_list {
+	static class ListNode {
+		int val;
+		ListNode next;
+
+		ListNode() {
+		}
+
+		ListNode(int val) {
+			this.val = val;
+		}
+
+		ListNode(int val, ListNode next) {
+			this.val = val;
+			this.next = next;
+		}
+	}
+
+	public static void main(String[] args) {
+		ListNode root = new ListNode(1);
+		root.next = new ListNode(2);
+		root.next.next = new ListNode(3);
+		root.next.next.next = new ListNode(4);
+		root.next.next.next.next = new ListNode(5);
+		reorder_list ob1= new reorder_list();
+		ob1.reorderList(root);
+		while(root!=null) {
+			System.out.print(root.val);
+			root=root.next;
+		}
+	}
+	public void reorderList(ListNode head) {
+		 if(head == null || head.next == null) return ;
+	        ListNode slowPtr = head, fastPtr = head;
+	        ListNode prev = head;
+			// splitting list
+	        while(fastPtr != null && fastPtr.next != null){
+	            prev = slowPtr;
+	            slowPtr = slowPtr.next;
+	            fastPtr = fastPtr.next.next;
+	        }
+	        prev.next = null;
+			// reverse
+	        ListNode rev = reverse(slowPtr);
+	        ListNode ptr = head;
+			// arrange alternatively
+	        while(ptr != null){
+	            ListNode t1 = ptr.next;
+	            ListNode t2 = rev.next;
+	            ptr.next = rev;
+	            if(t1 != null)
+	                rev.next = t1;
+	            ptr = t1;
+	            rev = t2;
+	        }
+	    }
+	 public ListNode reverse(ListNode head){
+	        ListNode p1 = head;
+	        ListNode p2 = head.next;
+	        p1.next = null;
+	        while(p2 != null){
+	            ListNode temp = p2.next;
+	            p2.next = p1;
+	            p1 = p2;
+	            p2 = temp;
+	        }
+	        return p1;
+	    }
+	 
+}