leetcode--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 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]);  
        return Math.max(helper(nums, 0, nums.length-2), helper(nums, 1, nums.length-1));  
    }
	
	public int helper(int[] nums,int start,int end){
		int n = end-start+1;
		if(n==0) return 0;
		if(n==1) return nums[start];
		int[] flag = new int[n];
		flag[0] = nums[start];
		flag[1] = Math.max(nums[start], nums[start+1]);		
		for(int i=start+2;i<=end;i++){
			flag[i-start] = Math.max(flag[i-start-2]+nums[i],flag[i-start-1]);			
		}
		return flag[n-1];
	}