Search a 2D Matrix II

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 in ascending from left to right.
• Integers in each column are sorted in ascending from top to bottom.

For example,
Consider the following matrix:

[
  [1,   4,  7, 11, 15],
  [2,   5,  8, 12, 19],
  [3,   6,  9, 16, 22],
  [10, 13, 14, 17, 24],
  [18, 21, 23, 26, 30]
]

Given target = 5, return true.
Given target = 20, return false.

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Method 1: slower scanning the lower bound and high bound. easy to understand, cleaner code.

 

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public boolean searchMatrix(int[][] matrix, int target) {         int x=0,y=matrix.length-1;         //binary search y         if(target<matrix[0][0])return false;         if(matrix.length==1&&matrix[0].length==1)             return target==matrix[0][0];                         while(x<matrix[0].length && y>=0){                         if(target>matrix[y][x]){                 x++;             }             else if(target<matrix[y][x]){                 y--;             }             else{                 return true;             }         }         return false;

 

Method 2: binary search on both x and y

to be continuued