Lap Pool (Introduction to convex hull)

Source: Internet
Author: User

Lap Pool time limit:MS | Memory limit:65535 KB Difficulty:4
Describe
There is a pasture, where there are many water supplies, and now the owner of the ranch wants to circle the water supply with a fence to prevent them from drinking water, the pools are labeled with their coordinates, and now you need to write a program that uses the shortest fence to circle the water supply units! (The fence is large enough and variable in length)
Input
The first line of input is N, which represents the test data in N Group (1<=n<=10)
The second line is M, which represents a total of M water supply units (3<=M<=100) for this group of test data.
The next M-line represents the horizontal ordinate of each water supply unit.
Output
Output each fence through the coordinate points of each water supply device, and according to the x-axis coordinate value from small to large output, if the x-axis coordinate value is the same, and then Yasuteru y-coordinate value from small to large output
Sample input
`140 01 12) 33 0`
Sample output
`0 02 33 0`

The following: the use of the characteristics of the difference, if the difference is negative is a clockwise turn, if it is counterclockwise, if the 0 is a common line;

Code:

`1#include <iostream>2#include <cstdio>3#include <cstring>4#include <cmath>5#include <algorithm>6 using namespacestd;7 structnode{8     intx, y;9Friendint operator<(Node A,node b) {Ten         if(a.x<b.x| | (A.X==B.X&AMP;&AMP;A.Y&LT;B.Y))return 1; One         Else return 0; A     }  - }; - intChaji (Node a,node b,node c) { the     return(b.x-a.x) * (C.Y-A.Y)-(B.Y-A.Y) * (c.x-a.x); - } -Node a[ the],ans[ the]; - intMain () { +     intn,m; -scanf"%d",&N); +      while(n--){ Ascanf"%d",&m); at          for(intI=0; i<m;i++) scanf ("%d%d",&a[i].x,&a[i].y); -Sort (a,a+m); -         intk=0; -          for(intI=0; i<m;i++){ -              while(k>1&&chaji (ans[k-2],ans[k-1],a[i]) <=0) k--; -ans[k++]=A[i]; in         } -         intt=K; to          for(intj=n-1; i>=0; i--){ +              while(K>t&&chaji (ans[k-2],ans[k-1],a[i]) <=0) k--; -ans[k++]=A[i]; the         } *k--; \$Sort (ans,ans+k);Panax Notoginseng          for(intI=0; i<k;i++) printf ("%d%d\n", ans[i].x,ans[i].y); -     } the     return 0; +}`

Lap Pool (Introduction to convex hull)

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