_213.java

package com.fishercoder.solutions;
/**213. House Robber II

 Note: This is an extension of House Robber.

After robbing those houses on that street,
 the thief has found himself a new place for his thievery
 so that he will not get too much attention.
 This time, all houses at this place are arranged in a circle.
 That means the first house is the neighbor of the last one.
 Meanwhile, the security system for these houses remain the same as for those in the previous street.

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.
*/
public class _213 {

    /**Another dp problem:
     * separate them into two cases:
     * 1. rob from house 1 to n-1, get max1
     * 2. rob from house 2 to n, get max2
     * take the max from the above two max*/
    public int rob(int[] nums) {
        if(nums == null || nums.length == 0) return 0;
        if(nums.length == 1) return nums[0];
        if(nums.length == 2) return Math.max(nums[0], nums[1]);
        int[] dp = new int[nums.length-1];
        
        //rob 1 to n-1
        dp[0] = nums[0];
        dp[1] = Math.max(nums[0], nums[1]);
        for(int i = 2; i < nums.length-1; i++){
            dp[i] = Math.max(dp[i-2] + nums[i], dp[i-1]);
        }
        int prevMax = dp[nums.length-2];
        
        //rob 2 to n
        dp = new int[nums.length-1];
        dp[0] = nums[1];
        dp[1] = Math.max(nums[1], nums[2]);
        for(int i = 3; i < nums.length; i++){
            dp[i-1] = Math.max(dp[i-3] + nums[i], dp[i-2]);
        }
        return Math.max(prevMax, dp[nums.length-2]);
    }

}