[LeetCode][JavaScript]Search a 2D Matrix

Search a 2D Matrix

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 from left to right.
• The first integer of each row is greater than the last integer of the previous row.

 

For example,

Consider the following matrix:

[
  [1,   3,  5,  7],
  [10, 11, 16, 20],
  [23, 30, 34, 50]
]

Given target = 3, return true.

https://leetcode.com/problems/search-a-2d-matrix/

 

 

 

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虽然是个二维数组，但是有序，当成一维数组二分，计算出row和col的下标。

如果错用两次二分，一次做行一次做列，写起来就很复杂了。

 1 /**
 2  * @param {number[][]} matrix
 3  * @param {number} target
 4  * @return {boolean}
 5  */
 6 var searchMatrix = function(matrix, target) {
 7     var m = matrix.length, n = matrix[0].length;
 8     var i  = 0, j = m * n - 1, middle, row, col, curr;
 9     while(i <= j){
10         middle = parseInt((i + j) / 2);
11         row = parseInt(middle / n);
12         col = middle % n;
13         curr = matrix[row][col];
14         if(target === curr){
15             return true;
16         }
17 
18         if(target > curr){
19             i = middle + 1; 
20         }else{
21             j = middle - 1;
22         }    
23     }
24     return false;
25 };

 

 

转载于:https://www.cnblogs.com/Liok3187/p/4676054.html