Find the closest place from the starting point

Question

Suppose we have the following task: we want to read a set of coordinates (x, y) and a name, and then sort them in order, increasing the distance from the origin (0, 0). Here is an algorithm that uses the simplest sorting of bubbles:

#include<iostream> #include <algorithm> using namespace std; struct point{ float x; float y; char name[20]; }; float dist(point p){ return px*p.x+py*py; } void sorting(point pt[],int n){ bool doMore = true; while (doMore) { doMore = false; // Assume no more passes unless exchange made. for (int i=0; i<n-1; i++) { if (dist(pt[i]) > dist(pt[i+1])) { // Exchange elements point temp = pt[i]; pt[i] = pt[i+1]; pt[i+1] = temp; doMore = true; // Exchange requires another pass. } } } } void display(point pt[],int n){ for (int i=0;i<n;i++){ cout<<pt[i].name<< " "; } } int main(){ point pts[1000]; int n=0; while (cin>>pts[n].name>>pts[n].x>>pts[n].y){ n++; } sorting(pts,n); display(pts,n); return 0; } 

But I want to write an STL sorting algorithm instead of sorting bubbles. How to do it?

I mean, how should I use the dist function in the STL sort algorithm?

Answer 1

The STL sort function std::sort can accept a custom comparison function (or function object) as an optional third argument. Therefore, if you have your elements, for example:

 vector<point> points; 

You can sort them by phone:

 sort(points.begin(), points.end(), my_comp); 

where my_comp() is a function with the following prototype:

 bool my_comp(const point &a, const point &b) 

Answer 2

 #include <algorithm> bool sort_by_dist(point const& p1, point const& p2) { return dist(p1) < dist(p2); } ... std::sort(pt, pt + n, sort_by_dist);