Search a 2D Matrix

bool searchMatrix(vector<vector<int>>& matrix, int target) {

int a=matrix.size();

int b= matrix[0].size();

int l=0,r=a*b-1,m=0,v;

while(l<=r){

m=(l+r)/2;

v=matrix[m/b][m%b];

if(target==v)

return true;

else if(target>v)

l=m+1;

else

r=m-1;

}

return false;

}