[Swift]LeetCode378. 有序矩陣中第K小的元素 | Kth Smallest Element in a Sorted Matrix

原文地址：http://www.javashuo.com/article/p-yduroxyn-cx.html 

Given a n x n matrix where each of the rows and columns are sorted in ascending order, find the kth smallest element in the matrix.

Note that it is the kth smallest element in the sorted order, not the kth distinct element.

Example:

matrix = [
   [ 1,  5,  9],
   [10, 11, 13],
   [12, 13, 15]
],
k = 8,

return 13. 

Note: 
You may assume k is always valid, 1 ≤ k ≤ n^2.

---

給定一個 n x n 矩陣，其中每行和每列元素均按升序排序，找到矩陣中第k小的元素。
請注意，它是排序後的第k小元素，而不是第k個元素。

示例:

matrix = [
   [ 1,  5,  9],
   [10, 11, 13],
   [12, 13, 15]
],
k = 8,

返回 13。

說明: 
你能夠假設 k 的值永遠是有效的, 1 ≤ k ≤ n^2。

---

320ms

 1 class Solution {
 2     func kthSmallest(_ matrix: [[Int]], _ k: Int) -> Int {
 3         var matrix = matrix
 4         var left:Int = matrix[0][0]
 5         var right:Int = matrix.last!.last!
 6         while (left < right)
 7         {
 8             var mid:Int = left + (right - left) / 2
 9             var cnt:Int = search_less_equal(&matrix, mid)
10             if cnt < k
11             {
12                 left = mid + 1
13             }
14             else
15             {
16                 right = mid
17             }
18         }
19         return left
20     }
21     
22     func search_less_equal(_ matrix:inout [[Int]], _ target: Int) -> Int
23     {
24         var n:Int = matrix.count
25         var i:Int = n - 1
26         var j:Int = 0
27         var res:Int = 0
28         while(i >= 0 && j < n)
29         {
30             if matrix[i][j] <= target
31             {
32                 res += i + 1
33                 j += 1
34             }
35             else
36             {
37                 i -= 1
38             }
39         }
40         return res
41     }
42 }

---

384ms

 1 class Solution {
 2     func kthSmallest(_ matrix: [[Int]], _ k: Int) -> Int {
 3         var tagArr = [Int]();
 4         var totalItems = [Int]();
 5         for itmes in matrix {
 6             for item in itmes {
 7                 totalItems.append(item);
 8             }
 9         }
10         totalItems.sort();
11         var num = totalItems[k-1];
12         return num;
13     }
14 }