Search a 2D Matrix II

c++

class Solution {
public:
bool searchMatrix(vector<vector<int>>& matrix, int target) {
if (matrix.empty()) return false;
if (target < matrix[0][0] || target > matrix.back().back())
return false;
int i = 0, j = matrix[0].size() - 1;
while (i < matrix.size() && j >= 0)
{
if (target == matrix[i][j])
return true;
//if target > matrix[i][j],then target must not appear in row: 0~i
else if (target > matrix[i][j])
++i;
//if target < matrix[i][j],then target must not appear in col: j~col
else
--j;
}
return false;
}
};