leetcode 74. 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.

分析：

写出一个高效的算法来搜索 m × n矩阵中的值。这个矩阵具有以下特性：

• 每行中的整数从左到右是排序的。
• 每行的第一个数大于上一行的最后一个整数。

这道题可以把二维数组里的数字当作是一个有序的列表，用二分法查找。

public class Solution {    public boolean searchMatrix(int[][] matrix, int target) {        if (matrix == null || matrix.length == 0) {            return false;        }        if (matrix[0] == null || matrix[0].length == 0) {            return false;        }                int row = matrix.length, column = matrix[0].length;        int start = 0, end = row * column - 1;                while (start + 1 < end) {            int mid = start + (end - start) / 2;            int number = matrix[mid / column][mid % column];            if (number == target) {                return true;            } else if (number < target) {                start = mid;            } else {                end = mid;            }        }                if (matrix[start / column][start % column] == target) {            return true;        } else if (matrix[end / column][end % column] == target) {            return true;        }                return false;            }}