240. 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.

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.

 

class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        // find if matrix == null or length is 0
        if(matrix == null || matrix.length==0){
             return false;
        }
        // find if matrix[0] == null or length is 0
        if(matrix[0]==null || matrix[0].length ==0){
              return false;
        }
        
        int row_end = matrix.length-1; 
        int column_end = matrix[0].length-1;
        
        if(matrix[0][0]>target || matrix[row_end][column_end]< target){
            return false;
        }
        
        int row_cur = row_end;
        int column_cur = 0;
        //start from last row and first column
        //if last row and first column is larger than target, move to the last row
        //if last row and first column is less than target, move to the next column
        while(row_cur>=0 && column_cur<matrix[0].length){
            if(matrix[row_cur][column_cur]>target){
                row_cur--;
            }
            else if(matrix[row_cur][column_cur]<target){
                column_cur++;
            }
            else if(matrix[row_cur][column_cur]==target){
                return true;
            }
        }
        
        return false;
        
    }
}