LeetCode 198. House Robber（小偷游戏）

原题网址：https://leetcode.com/problems/house-robber/

You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed, the only constraint stopping you from robbing each of them is that adjacent houses have security system connected and it
will automatically contact the police if two adjacent houses were broken into on the same night.

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.
方法一：动态规划。

public class Solution {
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[] max = new int[nums.length];
max[0] = nums[0];
max[1] = Math.max(nums[0], nums[1]);
for(int i=2; i<nums.length; i++) {
max[i] = Math.max(max[i-1], max[i-2] + nums[i]);
}
return max[nums.length-1];
}
}

方法二：在方法一基础上优化内存。

public class Solution {
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 max = 0, prev2 = nums[0], prev1 = Math.max(nums[0], nums[1]);
for(int i=2; i<nums.length; i++) {
max = Math.max(prev2 + nums[i], prev1);
prev2 = prev1;
prev1 = max;
}
return max;
}
}