Two-dimensional convex hull Template

# Include <stdio. h> # Include <Math. h> # Include <Algorithm> # Include <Iostream> Using   Namespace  STD;  Const   Int Maxn = 1000  ;  Struct  Point {  Int  X, Y ;}; point list [maxn]; Int  Stack [maxn], top;  Int Cross (point P0, Point P1, point P2) //  Calculate the cross product p0p1 x p0p2  {  Return (P1.x-Snapshot X) * (p2.y-Snapshot y)-(p1.y-Snapshot y) * (p2.x- Optional X );}  Double DIS (point P1, point P2) //  Calculate the P1P2 distance  {  Return SQRT (( Double ) (P2.x-p1.x) * (p2.x-p1.x) + (p2.y-p1.y) * (p2.y- P1.y ));}  Bool CMP (point P1, point P2) //  The polar ordering function. If the angle is the same, the distance is smaller than the previous one.  {  Int TMP = cross (list [ 0  ], P1, P2 );  If (TMP> 0 ) Return   True  ;  Else  If (TMP = 0 & DIS (list [ 0 ], P1) <DIS (list [ 0 ], P2 )) Return   True  ;  Else   Return   False  ;}  Void Init ( Int N) //  Enter and place the vertices at the bottom left of the page in list [0]. And performs polar sorting. {  Int  I, K; point P0; scanf (  "  % D  " , & List [ 0 ]. X, & list [ 0  ]. Y); returns x = List [ 0  ]. X; Policy = List [ 0  ]. Y; k = 0  ; For (I = 1 ; I <n; I ++ ) {Scanf (  "  % D  " , & List [I]. X ,& List [I]. y );  If (Optional Y> list [I]. Y) | (Optional Y = list [I]. Y) & (Optional X> List [I]. X) {returns x = List [I]. X; Policy = List [I]. Y; k = I ;}} list [k] = List [ 0  ]; List [  0 ] = P0; sort (list + 1 , List + N, CMP );}  Void Graham ( Int  N ){  Int  I;  If (N = 1 ) {Top = 0 ; Stack [0 ] = 0  ;}  If (N = 2  ) {Top = 1  ; Stack [  0 ] = 0  ; Stack [  1 ] = 1  ;}  If (N>2  ){  For (I = 0 ; I <= 1 ; I ++) stack [I] = I; top = 1  ;  For (I = 2 ; I <n; I ++ ){  While (Top> 0 & Cross (list [stack [Top- 1 ], List [stack [Top], list [I]) <= 0 ) Top -- ; Top ++ ; Stack [Top] = I ;}}}