leetcode：Search a 2D Matrix 【Java】

一、问题描述

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

.
二、问题分析

重要的是把线性下转换成矩阵元素下标

三、算法代码

public class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        int m = matrix.length;
		int n = matrix[0].length;
		int start = 0;
		int end = m * n - 1;
		int element = 0;
		while(start <= end){
			int middle = (start + end)/2;
			element = matrix[middle / n][middle % n];//把下标转换成矩阵元素
			if(element == target){
				return true;
			}
			if(element < target){
				start = middle + 1;
			}else{
				end = middle - 1;
			}
		}
        return false;
    }
}