Leetcode: Jianzhi offer 04 Search in two-dimensional array

In a n * m In a two-dimensional array , Each row is sorted in ascending order from left to right , Each column is sorted in ascending order from top to bottom . Please complete an efficient function , Enter such a two-dimensional array and an integer , Determine whether the array contains the integer .

Example :

The existing matrix matrix as follows ：

[
  [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.

Limit ：

• 0 <= n <= 1000

• 0 <= m <= 1000

Be careful ： This topic and the main station 240 The question is the same ：https://leetcode-cn.com/problems/search-a-2d-matrix-ii/

---

Their thinking

1. First, define the coordinates of the lower left corner ,
2. Then traverse the matrix from the lower left element ： If the current element > target, Then move up one line ; If the current element < target, Move one column to the right ; If the current element = target, Then return directly true that will do
3. Finally, after searching through the above loop , If not found equal to target The element of returns directly false that will do

Code

/** * @param {number[][]} matrix * @param {number} target * @return {boolean} */
var findNumberIn2DArray = function(matrix, target) {
    
    if(!matrix.length) return false;
    //  Define the coordinates of the lower left corner 
    let [row, col] = [matrix.length - 1, 0];
    const len = matrix[0].length;
    //  The coordinates are in the matrix , Just keep looking for 
    while (row >= 0 && col <= len - 1) {
    
        // item  Represents the current element 
        const item = matrix[row][col];
        if (item === target) {
    
            //  find , return true
            return true;
        } else if (item > target) {
    
            //  It's too big , Move up a line 
            row--;
        } else {
    
            //  Is too small , Move a column to the right 
            col++;
        }
    }
    return false;
};