Search a 2D Matrix

Method One:

Using Binary Search Once. The point is how to calculated the number's index. mtarix[<num> / nCol][<num> % nCol]

public class Solution {
    /**
     * @param matrix, a list of lists of integers
     * @param target, an integer
     * @return a boolean, indicate whether matrix contains target
     */
    public boolean searchMatrix(int[][] matrix, int target) {
        // write your code here
        if (matrix == null || matrix.length == 0) {
            return false;
        }
        
        if (matrix[0] == null || matrix[0].length == 0) {
            return false;
        }
        
        int nRow = matrix.length;
        int nCol = matrix[0].length;
        int start = 0;
        int end = nRow * nCol - 1;
        
        while (start + 1 < end) {
            int mid = start + (end - start) / 2;
            if (matrix[mid / nCol][mid % nCol] == target) {
                return true;
            } else if (matrix[mid / nCol][mid % nCol] < target) {
                start = mid;
            } else {
                end = mid;
            }
        }
        
        if (matrix[start / nCol][start % nCol] == target) {
            return true;
        } 
        if (matrix[end / nCol][end % nCol] == target) {
            return true;
        }
        return false;
    }
}

 

 

Method Two:
Binary Search Twice

public class Solution {
    /**
     * @param matrix, a list of lists of integers
     * @param target, an integer
     * @return a boolean, indicate whether matrix contains target
     */
    public boolean searchMatrix(int[][] matrix, int target) {
        // write your code here
        if (matrix == null || matrix.length == 0) {
            return false;
        }
        
        if (matrix[0] == null || matrix[0].length == 0) {
            return false;
        }
        
        int startRow = 0;
        int endRow = matrix.length - 1;
        while (startRow + 1 < endRow) {
            int mid = startRow + (endRow - startRow) / 2;
            if (matrix[mid][0] == target) {
                return true;
            } else if (matrix[mid][0] < target) {
                startRow = mid;
            } else {
                endRow = mid;
            }
        }
        
        int row = startRow;
        if (matrix[startRow][0] == target) {
            return true;
        }
        
        if(matrix[endRow][0] == target) {
            return true;
        }
        
        if(matrix[endRow][0] < target ) {
            row = endRow;
        } 
        
        int startCol = 0;
        int endCol = matrix[row].length - 1;
        while (startCol + 1  < endCol) {
            int mid = startCol + (endCol - startCol) / 2;
            if (matrix[row][mid] == target) {
                return true;
            } else if (matrix[row][mid] < target) {
                startCol = mid;
            } else {
                endCol = mid;
            }
        }
        
        if (matrix[row][startCol] == target) {
            return true;
        }
        
        if (matrix[row][endCol] == target) {
            return true;
        }
        
        return false;
    }
}