diff --git a/longest-substring-without-repeating-characters/PDKhan.cpp b/longest-substring-without-repeating-characters/PDKhan.cpp
new file mode 100644
index 000000000..b57a1719c
--- /dev/null
+++ b/longest-substring-without-repeating-characters/PDKhan.cpp
@@ -0,0 +1,20 @@
+class Solution {
+    public:
+        int lengthOfLongestSubstring(string s) {
+            int result = 0;
+            int start = 0;
+            unordered_map<char, int> map;
+    
+            for(int end = 0; end < s.length(); end++){
+                char ch = s[end];
+    
+                if(map.count(ch) && map[ch] >= start)
+                    start = map[ch] + 1;
+                
+                map[ch] = end;
+                result = max(result, end - start + 1);
+            }
+    
+            return result;
+        }
+    };
diff --git a/number-of-islands/PDKhan.cpp b/number-of-islands/PDKhan.cpp
new file mode 100644
index 000000000..891f19ead
--- /dev/null
+++ b/number-of-islands/PDKhan.cpp
@@ -0,0 +1,29 @@
+class Solution {
+    public:
+        void search(int r, int c, vector<vector<char>>& grid){
+            if(r < 0 || c < 0 || r >= grid.size() || c >= grid[r].size() || grid[r][c] == '0')
+                return;
+            
+            grid[r][c] = '0';
+    
+            search(r-1, c, grid);
+            search(r+1, c, grid);
+            search(r, c-1, grid);
+            search(r, c+1, grid);
+        }
+    
+        int numIslands(vector<vector<char>>& grid) {
+            int cnt = 0;
+    
+            for(int i = 0; i < grid.size(); i++){
+                for(int j = 0; j < grid[i].size(); j++){
+                    if(grid[i][j] == '1'){
+                        search(i, j, grid);
+                        cnt++;
+                    }
+                }
+            }
+    
+            return cnt;
+        }
+    };
diff --git a/reverse-linked-list/PDKhan.cpp b/reverse-linked-list/PDKhan.cpp
new file mode 100644
index 000000000..71ff745f8
--- /dev/null
+++ b/reverse-linked-list/PDKhan.cpp
@@ -0,0 +1,16 @@
+class Solution {
+    public:
+        ListNode* reverseList(ListNode* head) {
+            ListNode* new_head = NULL;
+    
+            while(head){
+                ListNode* next = head->next;
+    
+                head->next = new_head;
+                new_head = head;
+                head = next;
+            }
+    
+            return new_head;
+        }
+    };
diff --git a/set-matrix-zeroes/PDKhan.cpp b/set-matrix-zeroes/PDKhan.cpp
new file mode 100644
index 000000000..975b59e45
--- /dev/null
+++ b/set-matrix-zeroes/PDKhan.cpp
@@ -0,0 +1,46 @@
+class Solution {
+    public:
+        void setZeroes(vector<vector<int>>& matrix) {
+            int rows = matrix.size();
+            int cols = matrix[0].size();
+    
+            bool firstRowZero = false;
+            bool firstColZero = false;
+    
+            for(int j = 0; j < cols; j++){
+                if(matrix[0][j] == 0)
+                    firstRowZero = true;
+            }
+    
+            for(int i = 0; i < rows; i++){
+                if(matrix[i][0] == 0)
+                    firstColZero = true;
+            }
+    
+            for(int i = 1; i < rows; i++){
+                for(int j = 1; j < cols; j++){
+                    if(matrix[i][j] == 0){
+                        matrix[i][0] = 0;
+                        matrix[0][j] = 0;
+                    }
+                }
+            }
+    
+            for(int i = 1; i < matrix.size(); i++){
+                for(int j = 1; j < matrix[0].size(); j++){
+                    if(matrix[0][j] == 0 || matrix[i][0] == 0)
+                        matrix[i][j] = 0;
+                }        
+            }
+    
+            if(firstRowZero){
+                for(int j = 0; j < cols; j++)
+                    matrix[0][j] = 0;
+            }
+    
+            if(firstColZero){
+                for(int i = 0; i < rows; i++)
+                    matrix[i][0] = 0;
+            }
+        }
+    };
diff --git a/unique-paths/PDKhan.cpp b/unique-paths/PDKhan.cpp
new file mode 100644
index 000000000..aca265348
--- /dev/null
+++ b/unique-paths/PDKhan.cpp
@@ -0,0 +1,22 @@
+class Solution {
+    public:
+        int uniquePaths(int m, int n) {
+            vector<vector<int>> dp(m, vector<int>(n, 0));
+    
+            dp[0][0] = 1;
+    
+            for(int i = 1; i < m; i++)
+                dp[i][0] = 1;
+    
+            for(int j = 1; j < n; j++)
+                dp[0][j] = 1;
+    
+            for(int i = 1; i < m; i++){
+                for(int j = 1; j < n; j++){
+                    dp[i][j] = dp[i - 1][j] + dp[i][j - 1];
+                }
+            }
+    
+            return dp[m - 1][n - 1];
+        }
+    };