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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 = 
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;
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);
}
}
``````