Search a 2D Matrix

Search a 2D Matrix

Write an efficient algorithm that searches for a value in anm 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.

 

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