Adding the solutions

Knapsack.java

@@ -0,0 +1,19 @@
+ // TimeComplexity: O(n x W) 
+ // SpaceComplexity: O(W)
+
+  static int knapsack(int W, int[] val, int[] wt) {
+
+        // Initializing dp array
+        int[] dp = new int[W + 1];
+
+        // Taking first i elements
+        for (int i = 1; i <= wt.length; i++) {
+
+            // Starting from back, so that we also have data of
+            // previous computation of i-1 items
+            for (int j = W; j >= wt[i - 1]; j--) {
+                dp[j] = Math.max(dp[j], dp[j - wt[i - 1]] + val[i - 1]);
+            }
+        }
+        return dp[W];
+    }

TwoSum.java

@@ -0,0 +1,18 @@
+// TimeComplexity: O(n)
+// SpaceComplexity: O(n)
+// Explanation: I am iterating through the array and storing the elemnet in the hashmap with its index if the compliment is not found. If the compliment is found I am returning the compliment index and the current index.
+
+class Solution {
+    public int[] twoSum(int[] nums, int target) {
+        int n = nums.length;
+        HashMap<Integer, Integer> map = new HashMap<>();
+        for(int i=0; i<n; i++) {
+            if(map.containsKey(target-nums[i])) {
+                return new int[]{map.get(target-nums[i]), i};
+            }
+            map.put(nums[i], i);
+        }
+        return new int[2];
+
+    }
+}