func_code_string: #include <bits/stdc++.h>   using namespace std;   int n;   int x[1024], y[1024], c[1024];   int pts[1024];   int chull[1024], tp;   int chull_size;   int ans_l[1024], ans_r[1024], ans_len = 0;   void add_edge(int u, int v) {     ans_l[ans_len] = u;     ans_r[ans_len] = v;     ans_len++;   }   void print_ans() {     printf( %d n , ans_len);     for (int i = 0; i < ans_len; i++) printf( %d %d n , ans_l[i], ans_r[i]);   }   bool ccw(int i, int j, int k) {     return (x[i] * y[j] + x[j] * y[k] + x[k] * y[i] - x[j] * y[i] - x[k] * y[j] -             x[i] * y[k]) > 0;   }   int pivot;   bool comp_by_pivot(int i, int j) {     assert(i != pivot);     assert(j != pivot);     return ccw(pivot, i, j);   }   void run(int i, int j, int k, const vector<int> &inner, bool sep) {     if (inner.size() == 0) {       if (sep) {         ;       } else {         add_edge(j, k);       }     } else {       int pivot = -1;       for (int p : inner) {         if (pivot == -1 || ccw(j, p, pivot)) pivot = p;       }       vector<int> j_inner, k_inner;       for (int p : inner)         if (p != pivot) {           if (ccw(pivot, i, p))             j_inner.push_back(p);           else             k_inner.push_back(p);         }       if (c[pivot] == c[i]) {         run(j, pivot, i, j_inner, false);         run(k, i, pivot, k_inner, true);         if (!sep) add_edge(j, k);       } else {         run(i, j, pivot, j_inner, false);         run(i, pivot, k, k_inner, sep);       }     }   }   void run(int i, int j, int k, bool sep) {     assert(i != j && j != k && k != i);     assert(ccw(i, j, k));     vector<int> inner;     for (int l = 0; l < n; l++)       if (l != i && l != j && l != k && ccw(i, j, l) && ccw(j, k, l) &&           ccw(k, i, l)) {         inner.push_back(l);       }     run(i, j, k, inner, sep);   }   int main() {     scanf( %d , &n);     for (int i = 0; i < n; i++) {       scanf( %d %d %d , &x[i], &y[i], &c[i]);     }     if (n == 1) {       printf( 0 n );     } else if (n == 2) {       if (c[0] == c[1]) {         printf( 1 n );         printf( 0 1 n );       } else {         printf( 0 n );       }     } else {       pivot = 0;       for (int i = 1; i < n; i++)         if (x[i] < x[pivot] || (x[i] == x[pivot] && y[i] < y[pivot])) pivot = i;       for (int i = 0; i < n - 1; i++) pts[i] = (i < pivot ? i : i + 1);       sort(pts, pts + n - 1, comp_by_pivot);       chull[0] = pivot;       tp = 0;       for (int i = 0; i < n - 1; i++) {         int cur = pts[i];         while (tp >= 1 && (ccw(chull[tp - 1], chull[tp], cur) == false)) tp--;         chull[++tp] = cur;       }       chull_size = tp + 1;       int num_change = 0;       for (int i = 0; i < chull_size; i++)         if (c[chull[i]] != c[chull[(i + 1) % chull_size]]) num_change++;       if (num_change == 0) {         int c_chull = c[chull[0]];         int center_pivot = -1;         for (int i = 0; i < n; i++)           if (c[i] != c_chull) {             center_pivot = i;             break;           }         if (center_pivot == -1) {           printf( %d n , n - 1);           for (int i = 0; i < n - 1; i++) printf( %d %d n , pivot, pts[i]);         } else {           for (int i = 0; i < chull_size - 1; i++) {             run(center_pivot, chull[i], chull[i + 1], false);           }           run(center_pivot, chull[chull_size - 1], chull[0], true);           print_ans();         }       } else if (num_change == 2) {         int p1 = -1;         for (int i = 1; i < chull_size; i++)           if (c[chull[i - 1]] != c[chull[i]]) {             p1 = i;             break;           }         assert(p1 >= 1 && p1 < chull_size);         rotate(chull, chull + p1, chull + chull_size);         int p2 = -1;         for (int i = 1; i < chull_size; i++)           if (c[chull[i - 1]] != c[chull[i]]) {             p2 = i;             break;           }         for (int i = 0; i < p2 - 1; i++) {           run(chull[p2], chull[i], chull[i + 1], false);         }         for (int i = p2; i < chull_size - 1; i++) {           run(chull[0], chull[i], chull[i + 1], false);         }         print_ans();       } else {         assert(num_change % 2 != 1);         printf( Impossible n );       }     }     return 0;   }   