week 5 213. House Robber II

public class Solution {
   public int rob(int[] nums) {
    if(nums==null || nums.length==0)
        return 0; 
 
    if(nums.length==1)
        return nums[0];
 
    int max1 = robHelper(nums, 0, nums.length-2);
    int max2 = robHelper(nums, 1, nums.length-1);
 
    return Math.max(max1, max2);
}
 
public int robHelper(int[] nums, int i, int j){
    if(i==j){
        return nums[i];
    }
 
    int[] dp = new int[nums.length];
    dp[i]=nums[i];
    dp[i+1]=Math.max(nums[i+1], dp[i]);
 
    for(int k=i+2; k<=j; k++){
        dp[k]=Math.max(dp[k-1], dp[k-2]+nums[k]);    
    }
 
    return dp[j];
  }
}