240. Search a 2D Matrix II

Question

Write an efficient algorithm that searches for a value target in an m x n integer matrix 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 1:

Constraints:

• m == matrix.length
• n == matrix[i].length
• 1 <= n, m <= 300
• -109 <= matrix[i][j] <= 109
• All the integers in each row are sorted in ascending order.
• All the integers in each column are sorted in ascending order.
• -109 <= target <= 109

Algorithm

Same walk through as a question 378.Kth Smallest Element in a Sorted Matrix but much easier.

You start from left bottom corner element, if it's larger than the target, you go up otherwise you go right.

Code

class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        int m = matrix.length;
        int n = matrix[0].length;
        int i = m - 1, j = 0;
        while (i >= 0 && j < n) {
            if (matrix[i][j] > target) {
                i--;
            } else if (matrix[i][j] < target) {
                j++;
            } else {
                return true;
            }
        }
        
        return false;
    }
}