剑指Offer面试题3 & Leetcode74

剑指Offer面试题3 & Leetcode74

Search a 2D Matrix 二维数组中的查找

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.

解题思路

  考虑：如果数组中的数小于target，那么我们将会继续在该数右方和下方寻找target；如果数组中的数大于target,那么我们将会继续在该数左方和上方寻找target，这两种可能都会导致继续寻找的区域出现重叠。

  如果我们从数组右上角开始比较，就可以排除掉一个区域，不会出现重复，例如，如果该数小于target，因为该行中次数最大，所以只会去它下方继续寻找target。

Solution

public boolean searchMatrix(int[][] matrix, int target) {        if(matrix == null || matrix.length == 0)                return false;        int row = 0;        int column = matrix[0].length-1;        while(row<matrix.length && column >=0){            if(matrix[row][column] == target)                       return true;            else if(matrix[row][column] > target){                column--;            }else{                row++;            }        }        return false;    }