algorithm001
diff --git a/Week_03/id_57/leetcode_104_057.cpp b/Week_03/id_57/leetcode_104_057.cpp
@@ -0,0 +1,11 @@
+class Solution {
+public:
+    int maxDepth(TreeNode* root) {
+
+        if (root == NULL) return 0;
+        int left = maxDepth(root->left);
+        int right = maxDepth(root->right);
+        return max(left,right) + 1;
+
+    }
+};
diff --git a/Week_03/id_57/leetcode_703_057.cpp b/Week_03/id_57/leetcode_703_057.cpp
@@ -0,0 +1,22 @@
+class KthLargest {
+    priority_queue<int, vector<int>, greater<int> > pq;
+    int k;
+public:
+    KthLargest(int k, vector<int>& nums):k(k) {
+        for(auto n : nums)
+        {
+            pq.push(n);
+            if(pq.size() > k)
+                pq.pop();
+        }
+
+    }
+
+    int add(int val) {
+        pq.push(val);
+        if(pq.size() > k)
+            pq.pop();
+        return pq.top();
+
+    }
+};
diff --git a/Week_04/id_57/leetcode_169_057.cpp b/Week_04/id_57/leetcode_169_057.cpp
@@ -0,0 +1,20 @@
+class Solution {
+public:
+    int majorityElement(vector<int>& nums) {
+        int m = nums[0];
+        int c = 0;
+        for(int c = 0,i = 0; i < nums.size();i++)
+        {
+            if (c == 0)
+            {
+                m = nums[i]; c = 1;
+            }
+            else
+            {
+                m == nums[i] ? c++ : c--;
+            }
+        }
+        return m;
+
+    }
+};
diff --git a/Week_04/id_57/leetcode_784_057.cpp b/Week_04/id_57/leetcode_784_057.cpp
@@ -0,0 +1,34 @@
+class Solution {
+public:
+    void backtrade(string S, vector<string> &res,int i)
+    {
+        if (i > S.length())
+        {
+            res.push_back(S);
+            return;
+        }
+        if ((S[i]  >= 'A') && (S[i] <= 'Z'))
+        {            
+            backtrade(S,res,i+1);
+            S[i] += 32;    
+            backtrade(S,res,i+1);
+
+        }
+        else if ((S[i] >='a') && (S[i] <= 'z'))
+        {            
+            backtrade(S,res,i+1);
+            S[i] -= 32;    
+            backtrade(S,res,i+1);
+
+        }
+        else
+        {        
+            backtrade(S,res,i+1);
+        }
+    }
+    vector<string> letterCasePermutation(string S) {
+        vector<string> res;
+        backtrade(S,res,0);
+        return res;
+    }
+};