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240. Search a 2D Matrix II

Medium

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

Input: 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]], target = 5

Output: true

Example 2:

Input: 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]], target = 20

Output: false

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

Solution

public class Solution {
    public bool SearchMatrix(int[][] matrix, int target) {
        int r = 0;
        int c = matrix[0].Length - 1;
        while (r < matrix.Length && c >= 0) {
            if (matrix[r][c] == target) {
                return true;
            } else if (matrix[r][c] > target) {
                c--;
            } else {
                r++;
            }
        }
        return false;
    }
}

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