Merge pull request #704 from leoyang429/master

Add Disjoint Set in data_structure

data_structure/disjoint_set.cpp

@@ -0,0 +1,64 @@
+#include <iostream>
+#include <vector>
+
+using std::cout;
+using std::endl;
+using std::vector;
+
+vector<int> root, rnk;
+
+void CreateSet(int n) {
+  root = vector<int> (n+1);
+  rnk = vector<int> (n+1, 1);
+  for (int i = 1; i <= n; ++i) {
+    root[i] = i;
+  }
+}
+
+int Find(int x) {
+  if (root[x] == x) {
+    return x;
+  }
+  return root[x] = Find(root[x]);
+}
+
+bool InSameUnion(int x, int y) {
+  return Find(x) == Find(y);
+}
+
+void Union(int x, int y) {
+  int a = Find(x), b = Find(y);
+  if (a != b) {
+    if (rnk[a] < rnk[b]) {
+      root[a] = b;
+    } else if (rnk[a] > rnk[b]) {
+      root[b] = a;
+    } else {
+      root[a] = b;
+      ++rnk[b];
+    }
+  }
+}
+
+int main() {
+  // tests CreateSet & Find
+  int n = 100;
+  CreateSet(n);
+  for (int i = 1; i <= 100; ++i) {
+    if (root[i] != i) {
+      cout << "Fail" << endl;
+      break;
+    }
+  }
+  // tests InSameUnion & Union
+  cout << "1 and 2 are initially not in the same subset" << endl;
+  if (InSameUnion(1, 2)) {
+    cout << "Fail" << endl;
+  }
+  Union(1, 2);
+  cout << "1 and 2 are now in the same subset" << endl;
+  if (!InSameUnion(1, 2)) {
+    cout << "Fail" << endl;
+  }
+  return 0;
+}