equivalence class

__WIP/equivalence.cc

@@ -0,0 +1,34 @@
+#include <iostream>
+#include <vector>
+#include <cstdio>
+#include <algorithm>
+#include <functional>
+
+using namespace std;
+
+#define fst first
+#define snd second
+#define all(c) ((c).begin()), ((c).end())
+#define TEST(s) if (!(s)) { cout << __LINE__ << " " << #s << endl; exit(-1); }
+
+// specify operator == 
+template <class T, class F>
+void equivalence(vector<T> x, F eq) {
+  vector<int> parent(x.size());
+  for (int i = ; i < x.size(); ++i) {
+    parent[i] = i;
+    for (int j = 0; j < i; ++j) {
+      parent[j] = parent[parent[j]];
+      if (eq(x[i], x[j])) parent[parent[parent[j]]] = i;
+    }
+  }
+  for (int i = 0; i < x.size(); ++i) parent[i] = parent[parent[i]];
+
+  for (int i = 0; i < parent.size(); ++i) 
+    printf("%d %d \n", x[i], parent[i]);
+}
+
+int main() {
+  vector<int> x = {3,1,4,1,5,9,2,6,5,3,5,8,9};
+  equivalence(x, [&](int a, int b) { return a == b; });
+}