[Swift]LeetCode213. 打家劫舍 II | 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 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.

Example 1:

Input: [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: [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.

给定一个代表每个房屋存放金额的非负整数数组，计算你在不触动警报装置的情况下，能够偷窃到的最高金额。

示例 1:

输入: [2,3,2]
输出: 3
解释: 你不能先偷窃 1 号房屋（金额 = 2），然后偷窃 3 号房屋（金额 = 2）, 因为他们是相邻的。

示例 2:

输入: [1,2,3,1]
输出: 4
解释: 你可以先偷窃 1 号房屋（金额 = 1），然后偷窃 3 号房屋（金额 = 3）。
     偷窃到的最高金额 = 1 + 3 = 4 。

8ms

 1 class Solution {
 2     func rob(_ nums: [Int]) -> Int {
 3         guard nums.count != 1 else {
 4             return nums[0]
 5         }
 6
 7         return max(helper(nums, 0, nums.count - 2), helper(nums, 1, nums.count - 1))
 8     }
 9
10     fileprivate func helper(_ nums: [Int], _ start: Int, _ end: Int) -> Int {
11         if start > end {
12             return 0
13         }
14
15         var prev = 0, current = 0
16
17         for i in start...end {
18             (current, prev) = (max(prev + nums[i], current), current)
19         }
20
21         return current
22     }
23 }

 1 class Solution {
 2
 3     func rob(_ nums: [Int]) -> Int {
 4
 5         if nums.count == 0 { return 0 }
 6         if nums.count == 1 { return nums[0] }
 7
 8         return max(rob_nonCircular(nums, start: 0, end: nums.count - 1), rob_nonCircular(nums, start: 1, end: nums.count))
 9     }
10
11     func rob_nonCircular(_ nums: [Int], start: Int, end: Int) -> Int {
12         var a = nums[start], na = 0 // adjacent, non-adjacent
13
14         for i in (start+1)..<end {
15             let tmp = a
16             a = na + nums[i]
17             na = max(na, tmp)
18         }
19
20         return max(a, na)
21     }
22 }

 1 class Solution {
 2   var cache: [String: Int] = [:]
 3 func rob(_ nums: [Int]) -> Int {
 4     return max(rob(nums, startingAt: 1, endingAt: nums.count-1), rob(nums, startingAt: 0, endingAt: nums.count-2))
 5 }
 6
 7 func rob(_ nums: [Int], startingAt: Int, endingAt: Int) -> Int {
 8     if nums.count == 0 {
 9         return 0
10     }
11
12     if nums.count == 1 {
13         return nums[0]
14     }
15     if startingAt == endingAt {
16         return nums[startingAt]
17     }
18
19     if endingAt == startingAt+1 {
20         return max(nums[startingAt], nums[endingAt])
21     }
22
23     let first: Int
24     if let firstValue = cache[key(forStartingAt: startingAt, endingAt: endingAt-2)] {
25         first = firstValue
26     } else {
27         first = rob(nums, startingAt: startingAt, endingAt: endingAt-2)
28         cache[key(forStartingAt: startingAt, endingAt: endingAt-2)] = first
29     }
30
31     let second: Int
32     if let secondValue = cache[key(forStartingAt: startingAt, endingAt: endingAt-1)] {
33         second = secondValue
34     } else {
35         second = rob(nums, startingAt: startingAt, endingAt: endingAt-1)
36         cache[key(forStartingAt: startingAt, endingAt: endingAt-1)] = second
37     }
38
39     return max(nums[endingAt]+first, second)
40
41 }
42
43 func key(forStartingAt startingAt: Int, endingAt: Int) -> String {
44     return "StartingAt:" + String(startingAt) + "Ending At:" + String(endingAt)
45 }
46
47 }

 1 class Solution {
 2     func rob(_ nums: [Int]) -> Int {
 3         if nums.isEmpty {
 4             return 0
 5         }else if nums.count <= 3 {
 6             return nums.max()!
 7         }
 8
 9         return max(rob(nums, 0, nums.count-1), rob(nums, 1, nums.count))
10     }
11
12     func rob(_ nums : [Int], _ start : Int, _ end : Int) -> Int {
13         var currMax = nums[start]
14         var nextMax = max(currMax, nums[start+1])
15
16         for i in start+2..<end {
17             let tmp = nextMax
18             nextMax = max(currMax + nums[i], tmp)
19             currMax = tmp
20         }
21         return nextMax
22     }
23 }

 1 class Solution {
 2     func rob(_ nums: [Int]) -> Int {
 3         let n = nums.count
 4         if n == 0 { return 0 }
 5         if n == 1 { return nums[0] }
 6         if n == 2 { return max(nums[0], nums[1]) }
 7
 8          // 不考虑首尾相连，且偷第一个的情况
 9         var dp1 = [Int](repeating: 0, count: nums.count + 1)
10         // 不考虑首尾相连，且不偷第一个的情况
11         var dp2 = [Int](repeating: 0, count: nums.count + 1)
12
13         var result = [Int](repeating: 0, count: nums.count + 1)
14
15         dp1[0] = nums[0]
16         dp1[1] = nums[0]
17         for i in 2 ..< nums.count {
18             dp1[i] = max(dp1[i-1], dp1[i-2] + nums[i])
19         }
20
21         dp2[1] = nums[1]
22         for i in 2 ..< nums.count {
23             dp2[i] = max(dp2[i-1], dp2[i-2] + nums[i])
24         }
25
26         result[0] = nums[0]
27         for i in 1 ..< nums.count {
28             result[i] = max(dp1[i-1], dp2[i])
29         }
30         return result[nums.count - 1]
31
32     }
33 }

原文地址：https://www.cnblogs.com/strengthen/p/10197872.html