Added 2 solutions

Author: varunu28

Medium/Combinations.java

@@ -0,0 +1,27 @@
+class Solution {
+    public List<List<Integer>> combine(int n, int k) {
+        List<Integer> temp = new ArrayList<>();
+        List<List<Integer>> ans = new ArrayList<>();
+        helper(n, 1, temp, ans, k);
+        
+        return ans;
+    }
+    
+    private void helper(int n, int start, List<Integer> temp, List<List<Integer>> ans, int len) {
+        if (temp.size() == len) {
+            ans.add(new ArrayList<>(temp));
+            return;
+        }
+        
+        for (int i=start; i<=n; i++) {
+            // Choose
+            temp.add(i);
+            
+            // Explore
+            helper(n, i+1, temp, ans, len);
+            
+            // Un-choose
+            temp.remove(temp.size() - 1);
+        }
+    }
+} 

Medium/Diagonal Traverse.java

@@ -0,0 +1,67 @@
+class Solution {
+    public int[] findDiagonalOrder(int[][] matrix) {
+        if (matrix.length == 0 || matrix[0].length == 0) {
+            return new int[]{};
+        }
+        
+        int[] ans = new int[matrix.length * matrix[0].length];
+        int idx = 0;
+        
+        int i = 0;
+        boolean up = true;
+        
+		// First Triangle
+        while (i < matrix.length) {
+            int j = 0;
+            int tempI = i;
+            List<Integer> temp = new ArrayList<>();
+            while (j < matrix[0].length && tempI >= 0) {
+                temp.add(matrix[tempI][j]);
+                j++;
+                tempI--;
+            }
+            
+            if (!up) {
+                Collections.reverse(temp);
+            }
+            
+            for (int num : temp) {
+                ans[idx++] = num;
+            }
+            
+            up = !up;
+            i++;
+        }
+        
+        if (matrix[i-1].length < 2) {
+            return ans;
+        }    
+        
+        i--;
+        int j = 1;
+		// Second Triangle
+        while (j < matrix[0].length) {
+            int k = i;
+            List<Integer> temp = new ArrayList<>();
+            int tempJ = j;
+            while (k >= 0 && tempJ < matrix[0].length) {
+                temp.add(matrix[k][tempJ]);
+                k--;
+                tempJ++;
+            }
+            
+            if (!up) {
+                Collections.reverse(temp);
+            }
+            
+            for (int num : temp) {
+                ans[idx++] = num;
+            }
+            
+            up = !up;
+            j++;
+        }
+        
+        return ans;
+    }
+}