[Two sum and knapsack ]

Problem1.java

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+public class Problem1 {
+
+    // Time Complexity : O(n)
+    // Space Complexity : O(n)
+    // Did this code successfully run on Leetcode : yes
+    public int[] twoSum(int[] nums, int target) {
+        Map<Integer, Integer> map = new HashMap<>();
+
+        for (int i = 0; i < nums.length; i++) {
+            int complement = target - nums[i];
+            if (map.containsKey(complement)) {
+                return new int[] {map.get(complement), i};
+            }
+            map.put(nums[i], i);
+        }
+        return new int[] {};
+    }
+}

Problem2.java

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+public class Problem2 {
+
+    // Time Complexity : O(n * W_capacity)
+    // Space Complexity : O(W_capacity)
+    // Did this code successfully run on Leetcode : yes
+    public int knapsack(int W, int val[], int wt[]) {
+        int n = val.length;
+        int[] dp = new int[W + 1];
+        for (int i = 0; i < n; i++) {
+            for (int j = W; j >= wt[i]; j--) {
+                dp[j] = Math.max(dp[j], val[i] + dp[j - wt[i]]);
+            }
+        }
+
+        return dp[W];
+    }
+}