Search_a_2D_Matrix.cpp

/*
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
Consider the following matrix:
[
  [1,   3,  5,  7],
  [10, 11, 16, 20],
  [23, 30, 34, 50]
]
Given target = 3, return true.
*/
#include <vector>

using namespace std;

class Solution {
  public:
    /**
     * @param matrix, a list of lists of integers
     * @param target, an integer
     * @return a boolean, indicate whether matrix contains target
     */
    bool searchMatrix(vector<vector<int> >& matrix, int target) {
        // write your code here
        int rows = matrix.size();
        if (rows == 0) {
            return false;
        }
        int columns = matrix[0].size();
        if (columns == 0) {
            return false;
        }
        int i = 0;
        int j = columns - 1;
        while (i < rows && j >= 0) {
            if (matrix[i][j] == target) {
                return true;
            } else if (matrix[i][j] < target) {
                i++;
            } else {
                j--;
            }
        }
        return false;
    }
};