[Swift]LeetCode354. 俄羅斯套娃信封問題 | Russian Doll Envelopes

★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★
➤微信公衆號：山青詠芝（shanqingyongzhi）
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➤GitHub地址：https://github.com/strengthen/LeetCode
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★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★You have a number of envelopes with widths and heights given as a pair of integers (w, h). One envelope can fit into another if and only if both the width and height of one envelope is greater than the width and height of the other envelope.

What is the maximum number of envelopes can you Russian doll? (put one inside other)

Note:
Rotation is not allowed.

Example:

Input: [[5,4],[6,4],[6,7],[2,3]]
Output: 3 Explanation: The maximum number of envelopes you can Russian doll is  ([2,3] => [5,4] => [6,7]).3

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給定一些標記了寬度和高度的信封，寬度和高度以整數對形式 (w, h) 出現。當另外一個信封的寬度和高度都比這個信封大的時候，這個信封就能夠放進另外一個信封裏，如同俄羅斯套娃同樣。

請計算最多能有多少個信封能組成一組「俄羅斯套娃」信封（便可以把一個信封放到另外一個信封裏面）。

說明:
不容許旋轉信封。

示例:

輸入: envelopes = 
輸出: 3 
解釋: 最多信封的個數爲 [2,3] => [5,4] => [6,7]。[[5,4],[6,4],[6,7],[2,3]]3, 組合爲:

---

356ms

 1 class Solution {
 2     //二分法
 3     func maxEnvelopes(_ envelopes: [[Int]]) -> Int {
 4         var envelopes = envelopes
 5         var dp:[Int] = [Int]()
 6         envelopes.sort(by:sortArray)
 7         for i in 0..<envelopes.count
 8         {
 9             var left:Int = 0
10             var right:Int = dp.count
11             var t:Int = envelopes[i][1]
12             while(left < right)
13             {
14                 var mid:Int = left + (right - left) / 2
15                 if dp[mid] < t
16                 {
17                     left = mid + 1
18                 }
19                 else
20                 {
21                     right = mid
22                 }
23             }
24             if right >= dp.count
25             {
26                 dp.append(t)
27             }
28             else
29             {
30                 dp[right] = t
31             }            
32         }
33         return dp.count
34     }
35     
36     func sortArray(_ a:[Int],_ b:[Int]) -> Bool
37     {
38         if a[0] == b[0]
39         {
40             return a[1] > b[1]
41         }
42         return a[0] < b[0]
43     }
44 }

---

6948ms

 1 class Solution {
 2     func maxEnvelopes(_ envelopes: [[Int]]) -> Int {
 3         if envelopes.count == 0 { return 0 }
 4         let sorted = envelopes.sorted {
 5             return $0[0] < $1[0]
 6         }
 7         
 8         var dp: [Int] = [Int](repeating: 0, count: envelopes.count)
 9         var res = 0
10         for i in 0..<sorted.count {
11             dp[i] = 1
12             for j in 0..<i {
13                 // if i is bigger than j
14                 if sorted[i][0] > sorted[j][0] && sorted[i][1] > sorted[j][1] {
15                     dp[i] = max(dp[i], dp[j] + 1)
16                 }
17             }
18             res = max(res, dp[i])
19         }
20         return res
21     }
22 }