[leetcode]240. Search a 2D Matrix II

Posted 2020-06-29

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.

 

For 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.

Solution:

matrix[row][col]从右上角开始，向左下角移动。matrix[row][col] > target, 说明col列不存在target, matrix[row][col] < target， 说明row行不存在target

 1 bool searchMatrix(int** matrix, int matrixRowSize, int matrixColSize, int target) 
 2 {
 3     int row = 0;
 4     int col = matrixColSize - 1;
 5     
 6     while ((row < matrixRowSize) && (col >= 0))
 7     {
 8         if (matrix[row][col] == target)
 9             return true;
10         else if (matrix[row][col] > target)
11             col--;
12         else
13             row++;
14     }
15     
16     return false;
17 }