Day 37, 74 Search a 2D Matrix

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.
-------------------------------------------------------------
Do 2 binary searches
Note that start <= end
Searching a 2D Sorted Matrix Part

class Solution {
public:
    bool searchMatrix(vector<vector<int> > &matrix, int target) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
       // return false;
        int m = matrix.size();
        int n = matrix[0].size();
        int start = 0, end = m-1;
        if(target< matrix[0][0]) return false;  
        // binary search the first element of each row
        while (start <= end) {
            int mid = (start + end) / 2;
            if (matrix[mid][0] == target) {
                return true;
            }
            if (matrix[mid][0] > target) {
                end = mid - 1;
            }else {
                start = mid + 1;
            }
        }
        // binary search in that particular row
        int row = end;
        start = 0;
        end = n-1;
        while (start <= end) {
            int mid = (start + end) / 2; 
            if (matrix[row][mid] == target) {
                return true;
            }
            if (matrix[row][mid] > target) {
                end = mid - 1;
            }else {
                start = mid + 1;
            }
        }
        return false;
    }
};