213 House Robber II
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 an integer array nums representing the amount of money of each house, return the maximum amount of money you can rob tonight without alerting the police.
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 = [1,2,3]
Output: 3
此题类似 House Robber ， 环形街道取了第一个元素就不能取最后一个，取最后一个就不能取第一个，分两种情况求最优解。
class Solution {
public int rob(int[] nums) {
if(nums==null || nums.length==0) return 0;
if(nums.length==1) return nums[0];
return Math.max(rob(nums,0,nums.length-2),rob(nums,1,nums.length-1));
}
private int rob(int[] nums, int begin, int end){
int pre1=0, pre2=0, max=0;
for(int i=begin;i<=end;++i){
max=Math.max(pre1+nums[i],pre2);
pre1=pre2;
pre2=max;
}
return max;
}
}