Search a 2D Matrix


#1

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.

Example 1:

Input:
matrix = [
  [1,   3,  5,  7],
  [10, 11, 16, 20],
  [23, 30, 34, 50]
]
target = 3
Output: true

Example 2:

Input:
matrix = [
  [1,   3,  5,  7],
  [10, 11, 16, 20],
  [23, 30, 34, 50]
]
target = 13
Output: false

#2

The below code uses the properties of sorted matrix and runs in O(m+n) time.

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