[LeetCode] 74. Search a 2D Matrix

搜索一个二维矩阵。题意是给一个二维数组和一个target，问是否能在二维数组中找到这个target。

思路是将input convert成一个一维数组，然后用二分法做。这题因为convert完了之后，input是一个有序的一维数组，所以可以用二分法做。例子，

Example 1:

Input:
matrix = [
  [1,   3,  5,  7],
  [10, 11, 16, 20],
  [23, 30, 34, 50]
]
target = 3
Output: true

Example 2:

Input:
matrix = [
  [1,   3,  5,  7],
  [10, 11, 16, 20],
  [23, 30, 34, 50]
]
target = 13
Output: false

时间O(log mn), m和n是矩阵的长宽

空间O(1)

 1 /**
 2  * @param {number[][]} matrix
 3  * @param {number} target
 4  * @return {boolean}
 5  */
 6 var searchMatrix = function(matrix, target) {
 7     // corner case
 8     if (matrix === null || matrix.length === 0) {
 9         return false;
10     }
11 
12     // normal case
13     let row = matrix.length;
14     let col = matrix[0].length;
15     let start = 0;
16     let end = row * col - 1;
17     while (start <= end) {
18         let mid = Math.floor(start + (end - start) / 2);
19         let value = matrix[Math.floor(mid / col)][Math.floor(mid % col)];
20         if (value === target) {
21             return true;
22         } else if (value < target) {
23             start = mid + 1;
24         } else {
25             end = mid - 1;
26         }
27     }
28     return false;
29 };