Implement insert-delete-getrandom-o1-duplicates-allowed

name: insert-delete-getrandom-o1-duplicates-allowed
url: https://leetcode.com/problems/insert-delete-getrandom-o1-duplicates-allowed
difficulty: 3

time: 40 ms
time-rank: 96.84 %
time-complexity: O(1)

space: 26.7 MB
space-rank: 56.46 %
space-complexity: O(N)

Fixes #46

Signed-off-by: Christopher Friedt <[email protected]>

Author: cfriedt

insert-delete-getrandom-o1-duplicates-allowed-test.cpp

@@ -0,0 +1,65 @@
+/*
+ * Copyright (c) 2021, Christopher Friedt
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <gtest/gtest.h>
+
+#include "insert-delete-getrandom-o1-duplicates-allowed.cpp"
+
+using namespace std;
+
+TEST(InsertDeleteGetrandomO1DuplicatesAllowed, example1) {
+  RandomizedCollection c;
+
+  EXPECT_EQ(true, c.insert(1));
+  EXPECT_EQ(false, c.insert(1));
+  EXPECT_EQ(true, c.insert(2));
+
+  int n1s = 0;
+  int n2s = 0;
+  for (int i = 0; i < 1000; ++i) {
+    if (1 == c.getRandom()) {
+      ++n1s;
+      continue;
+    }
+    if (2 == c.getRandom()) {
+      ++n2s;
+      continue;
+    }
+  }
+
+  // around 66%
+  EXPECT_GE(n1s, 600);
+
+  EXPECT_EQ(true, c.remove(1));
+
+  n1s = 0;
+  n2s = 0;
+  for (int i = 0; i < 1000; ++i) {
+    if (1 == c.getRandom()) {
+      ++n1s;
+      continue;
+    }
+    if (2 == c.getRandom()) {
+      ++n2s;
+      continue;
+    }
+  }
+
+  // around 50%
+  EXPECT_GE(n1s, 475);
+}
+
+TEST(InsertDeleteGetrandomO1DuplicatesAllowed, example2) {
+  RandomizedCollection c;
+  EXPECT_EQ(true, c.insert(0));
+  EXPECT_EQ(true, c.remove(0));
+  EXPECT_EQ(true, c.insert(-1));
+  EXPECT_EQ(false, c.remove(0));
+
+  for (int i = 0; i < 10; ++i) {
+    EXPECT_EQ(-1, c.getRandom());
+  }
+}

insert-delete-getrandom-o1-duplicates-allowed.cpp

@@ -0,0 +1,106 @@
+/*
+ * Copyright (c) 2021, Christopher Friedt
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+// clang-format off
+// name: insert-delete-getrandom-o1-duplicates-allowed
+// url: https://leetcode.com/problems/insert-delete-getrandom-o1-duplicates-allowed
+// difficulty: 3
+// clang-format on
+
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+using namespace std;
+
+class RandomizedCollection {
+public:
+  RandomizedCollection() {}
+
+  /** Inserts a value to the collection. Returns true if the collection did not
+   * already contain the specified element. */
+  bool insert(int val) {
+
+    auto it = index.find(val);
+    bool unique;
+
+    if (index.end() == it) {
+      unique = true;
+    } else {
+      unique = false;
+    }
+
+    elements.push_back(val);
+    index[val].insert(elements.size() - 1);
+
+    return unique;
+  }
+
+  /** Removes a value from the collection. Returns true if the collection
+   * contained the specified element. */
+  bool remove(int val) {
+
+    auto it = index.find(val);
+    if (index.end() == it) {
+      return false;
+    }
+
+    int val_idx = *(it->second.begin());
+
+    // val2 is whatever is at the back / tail of elements
+    int val2_idx = elements.size() - 1;
+    int val2 = elements[val2_idx];
+
+    if (val2_idx == val_idx) {
+      // element is already at the back, so just
+      // pop it out and erase the back index
+      // O(1)
+      elements.pop_back();
+      // O(1)*O(1) = O(1)
+      index[val].erase(val_idx);
+      if (index[val].empty()) {
+        index.erase(val);
+      }
+      return true;
+    }
+
+    // swap values at the two indeces
+    swap(elements[val_idx], elements[val2_idx]);
+    // get rid of val
+    elements.pop_back();
+    index[val].erase(val_idx);
+    if (index[val].empty()) {
+      index.erase(val);
+    }
+
+    // update the index of the val2 instance that moved
+    index[val2].erase(val2_idx);
+    index[val2].insert(val_idx);
+
+    return true;
+  }
+
+  /** Get a random element from the collection. */
+  int getRandom() {
+    long pos = ::random() % elements.size();
+    return elements[pos];
+  }
+
+protected:
+  vector<int> elements;
+
+  // key is the "value" to be added / removed from the collection
+  // value is an set of indices where "value" is found in elements
+  unordered_map<int, unordered_set<int>> index;
+};
+
+/**
+ * Your RandomizedCollection object will be instantiated and called as such:
+ * RandomizedCollection* obj = new RandomizedCollection();
+ * bool param_1 = obj->insert(val);
+ * bool param_2 = obj->remove(val);
+ * int param_3 = obj->getRandom();
+ */