leetcode 90: Search a 2D Matrix

Search a 2D MatrixApr 7 '12

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.

public class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(matrix.length==0) return false;
        this.line = matrix.length;
        this.col = matrix[0].length;
        
        return binarySearch( matrix, target);
    }
    
    private boolean binarySearch( int [][] matrix, int target) {
        int low = 0;
        int high = line*col-1;
            
        while(low <= high) {
            int mid = (low + high) / 2;
            int midLine = mid / col;
            int midCol = mid % col;
            
            if( matrix[midLine][midCol] == target ) return true;
            else if( matrix[midLine][midCol] > target) {
                high = mid - 1;
            } else {
                low = mid + 1;
            }
        }
        
        return false;
    }
    
    private int line;
    private int col;
}