Search a 2D Matrix

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.

Analyse: Binary Search!!!

Runtime: 16ms. 

class Solution {
public:
    bool searchMatrix(vector<vector<int>>& matrix, int target) {
        if(matrix.size() == 0) return false;
        
        int m = matrix.size(), n = matrix[0].size();
        int low = 0, high = m * n - 1;
        
        while(low <= high){
            int mid = (low + high) / 2;
            int val = matrix[mid / n][mid % n];
            
            if(val < target) low = mid + 1;
            else if(val > target) high = mid - 1;
            else return true;
        }
        return false;
    }
};