213. House Robber II

Description

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.

Constraints

• 1 <= nums.length <= 100

• 0 <= nums[i] <= 1000

Approach

Links

• GeeksforGeeks

• Leetcode

• ProgramCreek

• YouTube

Examples

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

Solutions

Solution 1

/**
 * Time complexity : O(N)
 * Space complexity : O(1)
 */

class Solution {
    public int rob(int[] nums) {
        if(nums == null || nums.length == 0) return 0;
        
        int n = nums.length;
        
        if(n == 1) return nums[0];
        
        int max1 = robHelper(nums, 0, n-1);
        int max2 = robHelper(nums, 1, n);
        
        return Math.max(max1, max2);
    }
    
    private int robHelper(int[] nums, int start, int end) {
        int prevMax = 0,
            currMax = 0;
        
        for(int i = start; i < end; i++) {
            int tmp = currMax;
            currMax = Math.max(currMax, prevMax+nums[i]);
            prevMax = tmp;
        }
        
        return currMax;
    }
}

Follow up