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[leetcode]Search a 2D Matrix

2024-07-17 00:27:28   227人阅读

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.

算法思路：

本题肯定要用二分查找的，如果是一维数组就完美了，可惜是二维，不过没关系，可以将二维数组抽象成一维。继续按照一维来操作。

代码如下：

 1 public class Solution { 2     public boolean searchMatrix(int[][] matrix, int target) { 3         if(matrix == null || matrix.length == 0 || matrix[0].length == 0) return false; 4         int height = matrix.length; 5         int width = matrix[0].length; 6         int begin = 0, end = height * width - 1; 7         while(begin <= end){ 8             int mid = (begin + end) >> 1; 9             int i = mid / width;10             int j = mid % width;11             if(matrix[i][j] == target){12                 return true;13             }else if(matrix[i][j] < target){14                 begin = mid + 1;15             }else{16                 end = mid - 1;17             }18         }19         return false;        20     }21 }

 


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