[Leetcode]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.

class Solution {public:    /*algorihtm binary search        2-d matrix can be regarded as 1-d array.        so actually this is sorted array        we can use binary search to do the check        time O(log(m*n)) space O(1)    */    bool searchMatrix(vector<vector<int>>& matrix, int target) {        int m = matrix.size();        if(m < 1)return false;        int n = matrix[0].size();        if(n < 1)return false;        int l = 0,r = m*n; //[l,r)        while(l < r){            int mid = l + (r-l)/2;            int i = mid/n,j = mid%n;            if(matrix[i][j] == target)return true;            else if(matrix[i][j] > target)                r = mid; //because [l,r)            else l = mid + 1;        }        return false;    }};