search-a-2d-matrix-ii.js

/**
 * Search a 2D Matrix II
 *
 * 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.
 * 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
 *
 * If we stand on the top-right corner of the matrix and look diagonally,
 * it's kind of like a BST, we can go through this matrix to find the target like how we traverse the BST.
 */

/**
 * @param {number[][]} matrix
 * @param {number} target
 * @return {boolean}
 */
const searchMatrix = (matrix, target) => {
  if (!matrix || matrix.length === 0) {
    return false;
  }

  const m = matrix.length;
  const n = matrix[0].length;

  let i = 0;
  let j = n - 1;

  while (i < m && j >= 0) {
    if (target === matrix[i][j]) {
      return true;
    } else if (target < matrix[i][j]) {
      j--;
    } else {
      i++;
    }
  }

  return false;
};

export { searchMatrix };