74. Search a 2D Matrix

Write an efficient algorithm that searches for a value in an mxn 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, returntrue.

思路：当成一维数列看，二分法

public class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        if (matrix.length == 0) return false;

        int row = matrix.length;
        int col = matrix[0].length;

        int l = 0;
        int r = row*col-1;

        while (l<=r){
            int m = (l+r)/2;
            int m_row = m/col;
            int m_col = m%col;
            if (matrix[m_row][m_col]==target){
                return true;
            }
            else if (matrix[m_row][m_col]<target){
                l = m+1;
            }
            else if (matrix[m_row][m_col]>target){
                r = m-1;
            }
        }

        return false;
    }
}