240. Search a 2D Matrix II

Problem

Tags: Array, Binary Search, Divide and Conquer, Matrix

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:

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
• -10^9 <= matrix[i][j] <= 10^9
• All the integers in each row are sorted in ascending order.
• All the integers in each column are sorted in ascending order.
• -10^9 <= target <= 10^9

Code

JS

// 240. Search a 2D Matrix II (6/8/53841)
// Runtime: 300 ms (92.06%) Memory: 42.45 MB (94.54%) 

/**
 * @param {number[][]} matrix
 * @param {number} target
 * @return {boolean}
 */
function searchMatrix(matrix, target) {
    const h = matrix.length;
    const w = matrix[0].length;
    
    let i = 0, j = w - 1;
    while (i < h && j >= 0) {
        let val = matrix[i][j]
        if (val === target) return true;
        else {
            if (val > target) j--;
            else i++;
        }
    }
    
    return false;
};