Completed Competitive-Coding-2

Problem1.py

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+#https://leetcode.com/problems/two-sum/description/
+# Time Complexity  : O(n),single loop through the array
+# Space Complexity : O(n),HashMap stores up to n elements
+# LeetCode Status  : Accepted
+# Problems Faced   : None
+
+class Solution:
+    def twoSum(self, nums, target):
+
+        map = {}                                # Create an empty HashMap to store {number: index}
+
+
+        for i in range(len(nums)):              # Loop through each number one by one
+
+            complement = target - nums[i]       # Calculate what number we need to complete the pair  
+
+            if complement in map:               # Check if that number already exists in our map
+                return [map[complement], i]     # If found, return the stored index of complement and the current index i
+
+            map[nums[i]] = i                    # If not found, store current number and its index

Problem2.py

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+#https://www.geeksforgeeks.org/dsa/0-1-knapsack-problem-dp-10/
+# Time Complexity  : O(W), where W is the capacity of the knapsack. We traverse the dp array of size W once for each item.
+# Space Complexity : O(W), as we use a 1D array of size W+1
+
+# Problems Faced   : None
+def knapsack(W, val, wt):
+    i = len(wt)                                        # total number of items
+    dp = [0] * (W + 1)                                 # 1D array of size W+1, initialized to 0
+
+    for row in range(1, i + 1):                        # loop through each item
+        for j in range(W, wt[row - 1] - 1, -1):       # traverse capacity right to left, stop at item's weight
+
+            pick = dp[j - wt[row-1]] + val[row-1]     # pick current item: add its value + best with remaining capacity
+            notPick = dp[j]                            # skip current item: keep existing best value
+
+            dp[j] = max(pick, notPick)                 # store the better choice
+
+    return dp[W]                                       # answer: max value at full capacity
+
+if __name__ == "__main__":
+    val = [1, 2, 3]                                    # values of items
+    wt = [4, 5, 1]                                     # weights of items
+    W = 4                                              # max capacity of knapsack
+    print(knapsack(W, val, wt))                        # output: 3