House Robber II

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2020-10-14

213. House Robber II

Question:

You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed. All houses at this place are arranged in a circle. That means the first house is the neighbor of the last one. Meanwhile, adjacent houses have a 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 nums representing the amount of money of each house, return the maximum amount of money you can rob tonight without alerting the police.

Example 1:

Input: nums = [2,3,2]
Output: 3
Explanation: You cannot rob house 1 (money = 2) and then rob house 3 (money = 2), because they are adjacent houses.

Example 2:

Input: nums = [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 3:

Input: nums = [0]
Output: 0

Constraints:

1 <= nums.length <= 100
0 <= nums[i] <= 1000

Solution:

Check the max for two different rob situation, including the first house or last house.

class Solution {
    public int rob(int[] nums) {
        if (nums == null || nums.length == 0) return 0;
        if (nums.length == 1) return nums[0];
        int n = nums.length;
        return Math.max(robHelper(nums, 0, n - 2), robHelper(nums, 1, n - 1));
    }
    
    private int robHelper(int[] nums, int start, int end) {
        int prevRob = 0;
        int prevNotRob = 0; 
        for (int i = start; i <= end; i++) {
            int curr = prevNotRob + nums[i];
            prevNotRob = Math.max(prevRob, prevNotRob);
            prevRob = Math.max(curr, prevRob);
        }
        return Math.max(prevNotRob, prevRob);
    }
}