HouseRobberII.java

/*
 * 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.

 Notice

This is an extension of House Robber.

Example
nums = [3,6,4], return 6
 */
public class HouseRobberII {

    /**
     * @param nums: An array of non-negative integers.
     * return: The maximum amount of money you can rob tonight
     */
    public int houseRobber2(int[] nums) {
        return Math.max(rob(nums, 0, nums.length - 2), 
                rob(nums, 1, nums.length - 1));
    }

    public int rob(int[] nums, int start, int end) {
        if (nums.length == 1) {
            return nums[0];
        }
        int result = 0;
        for (int i = start, prev = 0; i <= end; ++i) {
            int tmp = result;
            result = Math.max(result, prev + nums[i]);
            prev = tmp;
        }
        return result;
    }

}