STONE(Lifting the Stone) spoj problem soluiton

HII guys this is totally geometry based problem there is nothing to code just use formula 

 LOGIC::how to find centroid of a polygon u can this concept or formula given below

The centroid of a non-self-intersecting closed polygon defined by n vertices (x₀,y₀), (x₁,y₁), ..., (x_n−1,y_n−1) is the point (C_x, C_y), where

and where A is the polygon's signed area,

.^[13]

In these formulas, the vertices are assumed to be numbered in order of their occurrence along the polygon's perimeter, and the vertex ( x_n, y_n ) is assumed to be the same as (x₀, y₀ ). Note that if the points are numbered in clockwise order the area A, computed as above, will have a negative sign; but the centroid coordinates will be correct even in this case

IF still u have problem to implement this u can refer my solution given below::::

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#include<bits/stdc++.h> #include <cstdio> #include <cstdlib> #include <cmath> #include <cassert> #include <algorithm> #include <vector> using namespace std; int main() { int t; scanf("%d",&t); while(t--) { int n,i; scanf("%d",&n); int x[n+1],y[n+1]; double ans1=0,ans2=0; for(i=0;i<n;i++) { scanf("%d %d",&x[i],&y[i]); } double A=0,cx=0,cy=0,p; x[n]=x[0]; y[n]=y[0]; for(i=0;i<=n-1;i++) { p=(x[i]*y[i+1])-(x[i+1]*y[i]); cx+=p*(x[i]+x[i+1]); cy+=p*(y[i]+y[i+1]); A+=p; } A/=2; cx/=(6*A); cy/=(A*6); if (fabs(cx) < 0.005 - 1e-9) cx = 0; if (fabs(cy) < 0.005 - 1e-9) cy = 0; printf("%.2f %.2f\n", cx + 1e-9 * (cx >= -1e-9 ? 1 : -1), cy + 1e-9 * (cy >= -1e-9 ? 1 : -1)); } }