Added house_robber.py

dynamic_programming/house_robber.py

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+"""
+Code for house robber problem LeetCode : 198 using dynamic programming (tabulation).
+"""
+
+### Question explanation:
+# Given array of numbers which says how much money you can steel form houses.
+# The only constraint is if you rob from adjacent houses, it will ring alarm to police.
+
+### My Approach with DP:
+# As starting with DP, I will explain the approach in recursion with memoization which is more intuitive.
+# At each node in recursion, we have counter which True or False
+# Starting from last house, we have 2 options 1) If choosen, counter=True will be passed in recursion.
+#                                             2) If not choosen, counter=False will be passes in recursion.
+# If choosen=True at current house means previous house is choose so you can't choose current house.
+# If choosen=False at current house means it is not choosen, it means you have option to choose or not current house.
+## Example nums=[1,2,3,1]
+
+### Last index value   (1,  counter=False) (as we are starting from here we are free to choose)
+#                         /          \
+###            (3,counter=True)     (3,counter=False)     (counter=True mean 1 is choosen,so avoid 3)
+#                      /                   /       \
+###        (2,counter=False)            (2,True)  (2,False)
+#  (here 2,False means 1 is choosen, so we avoid 3 and
+# as 3 is avoided now again we are free to choose at house 2)
+
+
+## Note: dp[i][0]=>0 is True and 1 is False in convention.
+def rob(nums):
+    def helper(nums, dp, i, j):
+        if i < 0:
+            return 0
+        if dp[i][j] != -1:
+            return dp[i][j]
+        if j == True:
+            dp[i][0] = helper(nums, dp, i - 1, False)
+            return dp[i][0]
+        else:
+            dp[i][1] = max(
+                nums[i] + helper(nums, dp, i - 1, True), helper(nums, dp, i - 1, False)
+            )
+            return dp[i][1]
+
+    dp = [[-1] * 2 for _ in range(0, len(nums))]
+    return helper(nums, dp, len(nums) - 1, False)
+
+
+if __name__ == "__main__":
+    nums = [2, 7, 9, 3, 1]
+    if not nums:
+        print("The list is empty")
+    else:
+        max_amount = rob(nums)
+        print(max_amount)