View Compilation Error

0_0_17597031_27938.cpp: In function 'int main()':
0_0_17597031_27938.cpp:20:71: error: 'swap' was not declared in this scope
             if(a[i].y1==a[i].y2&&a[i].x1>a[i].x2) swap(a[i].x1,a[i].x2);
                                                                       ^
0_0_17597031_27938.cpp:21:71: error: 'swap' was not declared in this scope
             if(a[i].x1==a[i].x2&&a[i].y1>a[i].y2) swap(a[i].y1,a[i].y2);
                                                                       ^
0_0_17597031_27938.cpp:29:64: error: 'max' was not declared in this scope
                                 if(a[p].y1>=max(a[i].y1,a[j].y1)&&a[p].y1<=min(a[i].y2,a[j].y2))
                                                                ^
0_0_17597031_27938.cpp:29:95: error: 'min' was not declared in this scope
                                 if(a[p].y1>=max(a[i].y1,a[j].y1)&&a[p].y1<=min(a[i].y2,a[j].y2))
                                                                                               ^