Completed Competitive-Coding-2

Knapsack01.java

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+// Idea is to use pick and no pick elements to fill the knapsack
+// Use bottom up - DP array to store sub problem results and use them to solve larger problems  
+// Time Complexity: O(n)
+// Space Complexity: O(n)
+public class Knapsack01{
+
+        public int knapsack(int W, int[] val, int[] wt,int index) {
+        int n = wt.length;
+        int[][] dp = new int[n + 1][W + 1];
+
+        for (int i = 0; i <= n; i++) {
+            for (int j = 0; j <= W; j++) {
+                // If there is no item or the knapsack's capacity is 0
+                if (i == 0 || j == 0)
+                    dp[i][j] = 0;
+                else {
+                    int pick = 0;
+                    // Pick ith item if it does not exceed the capacity of knapsack
+                    if (wt[i - 1] <= j)
+                        pick = val[i - 1] + dp[i - 1][j - wt[i - 1]];
+                    int notPick = dp[i - 1][j];
+                    dp[i][j] = Math.max(pick, notPick);
+                }
+            }
+        }
+        return dp[n][W];
+        }
+}

TwoSumProblem.java

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+import java.util.HashMap;
+
+//Idea is to use Hashmap to store the value and index.
+//While inserting into the hashmap we simultaneously check for the compliment value (target-current value) 
+// Time Complexity: O(n)
+// Space Complexity: O(n)
+public class TwoSumProblem{
+
+        public int[] twoSum(int[] nums, int target) {
+        HashMap<Integer,Integer> hm = new HashMap<Integer,Integer>();
+        for(int i=0;i<nums.length;i++)
+        {
+            if(hm.containsKey(target-nums[i]))
+            {
+                return new int[]{i,hm.get(target-nums[i])};
+            }
+            else
+            {
+                hm.put(nums[i], i);
+            }
+        }
+        return new int[]{-1,-1};
+    }
+}