Leetcode Problem 198 House Robber.txt

198. House Robber

You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed, the only constraint stopping you from robbing each of them is that adjacent houses have security system connected and it will automatically contact the police if two adjacent houses were broken into on the same night.

Given a list of non-negative integers representing the amount of money of each house, determine the maximum amount of money you can rob tonight without alerting the police.

Example 1:

Input: [1,2,3,1]
Output: 4
Explanation: Rob house 1 (money = 1) and then rob house 3 (money = 3).
             Total amount you can rob = 1 + 3 = 4.
Example 2:

Input: [2,7,9,3,1]
Output: 12
Explanation: Rob house 1 (money = 2), rob house 3 (money = 9) and rob house 5 (money = 1).
             Total amount you can rob = 2 + 9 + 1 = 12.



Hint to solve: Recursive problem. At every point we can rob the current house or not which is decided by the max value.
If we rob the current house then recurse from index = index+2
If we don't rob the current house then recurse from index = index+1
Take max at that point.

To improve the algorithm speed use memoization.


class Solution:
    def rob(self, nums: List[int]) -> int:
        self.memo = [None]*len(nums)
        return self.recursive_rob(nums, 0)
    
    def recursive_rob(self,nums, currentHouseIndex):
        if(currentHouseIndex >= len(nums)):
            return 0
        
        if(self.memo[currentHouseIndex-1] != None):
            return self.memo[currentHouseIndex-1]
        
        result =  max(self.recursive_rob(nums, currentHouseIndex+2) + nums[currentHouseIndex],
                      self.recursive_rob(nums, currentHouseIndex+1))
        
        self.memo[currentHouseIndex-1] = result
        
        return result