Leetcode刷题记—— Search a 2D Matrix(在二维数组里查找)

一、题目叙述：

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.

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二、解题思路：

本题很简单，使用二分查找即可，只是比较时需要将mid值转换为数组横纵坐标即可，通过将mid/列数得到横坐标，mid%列数得到纵坐标即可。

三、源码：

public class Solution{    public boolean searchMatrix(int[][] matrix, int target)    {            int x = matrix.length;        if (x == 0) return false;        int y = matrix[0].length;        //int length = x * y;        int lo = 0;        int hi = x * y - 1;        while (lo <= hi)        {        int mid = lo + (hi - lo) / 2;        if (matrix[mid / y][mid % y] < target) lo = mid + 1;        else if (matrix[mid / y][mid % y] > target) hi = mid - 1;        else return true;        }        return false;    }    public static void main(String args[])    {    int[][] matrix = {};    Solution solution = new Solution();    System.out.println(solution.searchMatrix(matrix, 9));        }}