Leetcode 74: Search a 2D Matrix

Posted 2020-10-14 Keep walking

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 from left to right.
• The first integer of each row is greater than the last integer of the previous row.

 

For example,

Consider the following matrix:

[
  [1,   3,  5,  7],
  [10, 11, 16, 20],
  [23, 30, 34, 50]
]

Given target = 3, return true.

 

 1 public class Solution {
 2     public bool SearchMatrix(int[,] matrix, int target) {
 3         int m = matrix.GetLength(0), n = matrix.GetLength(1);
 4         int low = 0, high = m * n;
 5         
 6         while (low < high)
 7         {
 8             int mid = low + (high - low) / 2;
 9             int r = mid / n, c = mid % n;
10             
11             if (matrix[r, c] == target)
12             {
13                 return true;
14             }
15             else if (matrix[r, c] > target)
16             {
17                 high = mid;
18             }
19             else
20             {
21                 low = mid + 1;
22             }                
23         }
24         
25         return false;
26     }
27 }