Sst Palindrome LL

src/main/java/Rotate Image

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+--------------------------------------------------------------
+@Sayak
+Rotate the image by 90 degrees (clockwise).
+Given input matrix =
+[
+  [ 8, 1, 9,12],
+  [ 2, 4, 8,10],
+  [13, 3, 6, 7],
+  [18,14,12,16]
+], 
+
+rotate the input matrix in-place such that it becomes:
+[
+  [18,13, 2, 8],
+  [14, 3, 4, 1],
+  [12, 6, 8, 9],
+  [16, 7,10,12]
+]
+
+    The solution can be achieved int two steps:
+    1) Transpose the matrix
+    2) Reverse the matrix rows start<->end , start++, end--
+
+--------------------------------------------------------------
+
+class Solution {
+    public void rotate(int[][] matrix) {
+
+        int n= matrix.length;
+        for(int i=0;i<n;i++)
+        {
+            for(int j=i;j<n;j++)
+            {
+                int temp=matrix[i][j];
+                matrix[i][j]=matrix[j][i];
+                matrix[j][i]=temp;
+            }
+        }
+
+        for(int i=0;i<n;i++)
+        {
+            for(int j=0;j<(n/2);j++)
+            {
+                int temp=matrix[i][j];
+                matrix[i][j]=matrix[i][n-1-j];
+                matrix[i][n-1-j]=temp;
+            }
+        }
+    }
+}

src/main/java/Valid Palindrome(String)

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+--------------------------------------------------------------------------------------------------------------
+@Sayak
+Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.
+
+Note: For the purpose of this problem, we define empty string as valid palindrome.
+
+Example 1:
+
+Input: "A man, a plan, a canal: Panama"
+Output: true
+Example 2:
+
+Input: "race a car"
+Output: false
+---------------------------------------------------------------------------------------------------------------
+
+
+class Solution {
+    public boolean isPalindrome(String s) {
+
+        String fs="";
+        for(char c:s.toCharArray())
+        {
+            if(Character.isDigit(c)||Character.isLetter(c)){
+                fs+=c;
+            }
+        }
+
+        fs=fs.toLowerCase();
+        int ptr_a=0;
+        int ptr_b=fs.length()-1;
+
+        while(ptr_a<=ptr_b)
+        {
+            if(fs.charAt(ptr_a)!=fs.charAt(ptr_b)){
+                return false;
+            }
+            ptr_a++;
+            ptr_b--;
+        }
+       return true; 
+    }
+
+}

src/test/java/Palindrome LinkedList

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+------------------------------------------------------------
+@Sayak
+Given a singly linked list, determine if it is a palindrome.
+
+Example 1:
+Input: 1->2
+Output: false
+
+Example 2:
+Input: 1->2->2->1
+Output: true
+-----------------------------------------------------------
+
+
+/**
+ * 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; }
+ * }
+ */
+class Solution {
+    public boolean isPalindrome(ListNode head) {
+
+        ListNode slow=head;
+        ListNode fast=head;
+
+        while(fast!=null && fast.next!=null)
+        {
+            fast=fast.next.next;
+            slow=slow.next;
+        }
+        slow=reversed(slow);
+        fast=head;
+
+
+        while(slow!=null)
+        {
+            if(slow.val!=fast.val)
+            {
+                return false;
+            }
+            slow=slow.next;
+            fast=fast.next;
+        }
+        return true;
+
+    }
+        public ListNode reversed(ListNode head)
+    {
+        ListNode pnode=null;
+        ListNode nnode=head;
+        while(head!=null)
+        {
+            nnode=nnode.next;
+            head.next=pnode;
+            pnode=head;
+            head=nnode;
+        }
+        return pnode;
+    }
+
+}