[Swift]LeetCode240. 搜索二维矩阵 II | Search a 2D Matrix II

发布时间：2020-12-14 05:07:43 所属栏目：百科来源：网络整理

导读：Write an efficient algorithm that searches for a value in an? m ?x? n ?matrix. This matrix has the following properties: Integers in each row are sorted in ascending from left to right. Integers in each column are sorted in ascending from

Write an efficient algorithm that searches for a value in an?m?x?n?matrix. This matrix has the following properties:

Integers in each row are sorted in ascending from left to right.
Integers in each column are sorted in ascending from top to bottom.

Example:

Consider the following matrix:

[
  [1,4,7,11,15],[2,5,8,12,19],[3,6,9,16,22],[10,13,14,17,24],[18,21,23,26,30]
]

Given?target?=?5,return?true.

Given?target?=?20,return?false.

编写一个高效的算法来搜索?m?x?n?矩阵 matrix 中的一个目标值 target。该矩阵具有以下特性：

每行的元素从左到右升序排列。
每列的元素从上到下升序排列。

示例:

现有矩阵 matrix 如下：

[
  [1,30]
]

给定 target?=?5，返回?true。

给定?target?=?20，返回?false。

328ms

 1 class Solution {
 2     func searchMatrix(_ matrix: [[Int]],_ target: Int) -> Bool {
 3         // start at top right
 4         if matrix.count < 1 || matrix[0].count < 1 { return false }
 5         
 6         let rows = matrix.count,cols = matrix[0].count
 7         var r = 0,c = cols - 1
 8         
 9         while c >= 0,r < rows {
10             let num = matrix[r][c]
11             if num == target {
12                 return true
13             } else if num < target {
14                 r += 1
15             } else {
16                 c -= 1
17             }
18         }
19         
20         return false
21     }
22 }

332ms

 1 class Solution {
 2     func searchMatrix(_ matrix: [[Int]],_ target: Int) -> Bool {
 3     guard matrix.count > 0,matrix[0].count > 0 else {
 4         return false
 5     }
 6     
 7     let m = matrix.count
 8     let n = matrix[0].count
 9     
10     if target < matrix[0][0] || target > matrix[m-1][n-1] {
11         return false
12     }
13     
14     var i = m-1,j = 0
15     
16     while i >= 0,j < n {
17         if matrix[i][j] == target {
18             return true
19         } else if matrix[i][j] > target {
20             i -= 1
21         } else {
22             j += 1
23         }
24     }
25     
26     return false
27     }
28 }

332ms

 1 class Solution {
 2     func searchMatrix(_ matrix: [[Int]],_ target: Int) -> Bool {
 3         guard !matrix.isEmpty && !matrix[0].isEmpty else {
 4             return false
 5         }
 6 
 7         var row = 0
 8         var column = matrix[0].count - 1
 9         while column >= 0 && row < matrix.count {
10             if matrix[row][column] > target {
11                 column -= 1
12             } else if matrix[row][column] < target {
13                 row += 1
14             } else {
15                 return true
16             }
17         }
18 
19         return false
20     }
21 }

340ms

 1 class Solution {
 2     func searchMatrix(_ matrix: [[Int]],_ target: Int) -> Bool {
 3 
 4         guard matrix.count > 0,matrix[0].count > 0 else { return false }
 5         var m = matrix.count,n = matrix[0].count
 6         var i = m-1,j = 0
 7         while true {
 8             if matrix[i][j] == target { return true }
 9             else if matrix[i][j] < target { j += 1 }
10             else {
11                 i -= 1
12             }
13             if i < 0 || j >= n { return false }
14         }
15         return false
16     }
17 }

348ms

 1 class Solution {
 2     func searchMatrix(_ matrix: [[Int]],_ target: Int) -> Bool {
 3         for i in 0..<matrix.count {
 4             for j in stride(from: matrix[i].count,to: 0,by: -1) {
 5                     if matrix[i][j - 1] == target {
 6                         return true
 7                     }
 8             }
 9         }
10         
11         return false 
12     }
13 }

（编辑：李大同）

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