chore: import upstream snapshot with attribution

hashing/linear_probing_hash_table.cpp

@@ -0,0 +1,277 @@
+/**
+ * @file
+ * @author [achance6](https://github.com/achance6)
+ * @author [Krishna Vedala](https://github.com/kvedala)
+ * @brief Storage mechanism using [linear probing
+ * hash](https://en.wikipedia.org/wiki/Linear_probing) keys.
+ * @note The implementation can be optimized by using OOP style.
+ */
+#include <iostream>
+#include <vector>
+
+/**
+ * @addtogroup open_addressing Open Addressing
+ * @{
+ * @namespace linear_probing
+ * @brief An implementation of hash table using [linear
+ * probing](https://en.wikipedia.org/wiki/Linear_probing) algorithm.
+ */
+namespace linear_probing {
+// fwd declarations
+using Entry = struct Entry;
+bool putProber(const Entry& entry, int key);
+bool searchingProber(const Entry& entry, int key);
+void add(int key);
+
+// Undocumented globals
+int notPresent;
+std::vector<Entry> table;
+int totalSize;
+int tomb = -1;
+int size;
+bool rehashing;
+
+/** Node object that holds key */
+struct Entry {
+    explicit Entry(int key = notPresent) : key(key) {}  ///< constructor
+    int key;                                            ///< key value
+};
+
+/**
+ * @brief Hash a key. Uses the STL library's `std::hash()` function.
+ *
+ * @param key value to hash
+ * @return hash value of the key
+ */
+size_t hashFxn(int key) {
+    std::hash<int> hash;
+    return hash(key);
+}
+
+/** Performs linear probing to resolve collisions
+ * @param key key value to hash
+ * @return hash value of the key
+ */
+int linearProbe(int key, bool searching) {
+    int hash = static_cast<int>(hashFxn(key));
+    int i = 0;
+    Entry entry;
+    do {
+        int index = static_cast<int>((hash + i) % totalSize);
+        entry = table[index];
+        if (searching) {
+            if (entry.key == notPresent) {
+                return notPresent;
+            }
+            if (searchingProber(entry, key)) {
+                std::cout << "Found key!" << std::endl;
+                return index;
+            }
+            std::cout << "Found tombstone or equal hash, checking next"
+                      << std::endl;
+            i++;
+        } else {
+            if (putProber(entry, key)) {
+                if (!rehashing) {
+                    std::cout << "Spot found!" << std::endl;
+                }
+                return index;
+            }
+            if (!rehashing) {
+                std::cout << "Spot taken, looking at next" << std::endl;
+            }
+            i++;
+        }
+        if (i == totalSize) {
+            std::cout << "Linear probe failed" << std::endl;
+            return notPresent;
+        }
+    } while (entry.key != notPresent);
+    return notPresent;
+}
+
+/** Finds empty spot
+ * @param entry instance to check in
+ * @param key key value to hash
+ * @return hash value of the key
+ */
+bool putProber(const Entry& entry, int key) {
+    if (entry.key == notPresent || entry.key == tomb) {
+        return true;
+    }
+    return false;
+}
+
+/** Looks for a matching key
+ * @param entry instance to check in
+ * @param key key value to hash
+ * @return hash value of the key
+ */
+bool searchingProber(const Entry& entry, int key) {
+    if (entry.key == key) {
+        return true;
+    }
+    return false;
+}
+
+/** Function to displays the table
+ * @returns none
+ */
+void display() {
+    for (int i = 0; i < totalSize; i++) {
+        if (table[i].key == notPresent) {
+            std::cout << " Empty ";
+        } else if (table[i].key == tomb) {
+            std::cout << " Tomb ";
+        } else {
+            std::cout << " ";
+            std::cout << table[i].key;
+            std::cout << " ";
+        }
+    }
+    std::cout << std::endl;
+}
+
+/** Rehashes the table into a bigger table
+ * @returns None
+ */
+void rehash() {
+    // Necessary so wall of add info isn't printed all at once
+    rehashing = true;
+    int oldSize = totalSize;
+    std::vector<Entry> oldTable(table);
+    // Really this should use the next prime number greater than totalSize *
+    // 2
+    totalSize *= 2;
+    table = std::vector<Entry>(totalSize);
+    for (int i = 0; i < oldSize; i++) {
+        if (oldTable[i].key != -1 && oldTable[i].key != notPresent) {
+            size--;  // Size stays the same (add increments size)
+            add(oldTable[i].key);
+        }
+    }
+    // delete[] oldTable;
+    rehashing = false;
+    std::cout << "Table was rehashed, new size is: " << totalSize << std::endl;
+}
+
+/** Adds entry using linear probing. Checks for load factor here
+ * @param key key value to hash and add
+ */
+void add(int key) {
+    int index = linearProbe(key, false);
+    table[index].key = key;
+    // Load factor greater than 0.5 causes resizing
+    if (++size / static_cast<double>(totalSize) >= 0.5) {
+        rehash();
+    }
+}
+
+/** Removes key. Leaves tombstone upon removal.
+ * @param key key value to hash and remove
+ */
+void remove(int key) {
+    int index = linearProbe(key, true);
+    if (index == notPresent) {
+        std::cout << "key not found" << std::endl;
+    }
+    std::cout << "Removal Successful, leaving tomb" << std::endl;
+    table[index].key = tomb;
+    size--;
+}
+
+/** Information about the adding process
+ * @param key key value to hash and add
+ */
+void addInfo(int key) {
+    std::cout << "Initial table: ";
+    display();
+    std::cout << std::endl;
+    std::cout << "hash of " << key << " is " << hashFxn(key) << " % "
+              << totalSize << " == " << hashFxn(key) % totalSize;
+    std::cout << std::endl;
+    add(key);
+    std::cout << "New table: ";
+    display();
+}
+
+/** Information about removal process
+ * @param key key value to hash and remove
+ */
+void removalInfo(int key) {
+    std::cout << "Initial table: ";
+    display();
+    std::cout << std::endl;
+    std::cout << "hash of " << key << " is " << hashFxn(key) << " % "
+              << totalSize << " == " << hashFxn(key) % totalSize;
+    std::cout << std::endl;
+    remove(key);
+    std::cout << "New table: ";
+    display();
+}
+}  // namespace linear_probing
+/**
+ * @}
+ */
+
+using linear_probing::Entry;
+using linear_probing::table;
+using linear_probing::totalSize;
+
+/** Main function
+ * @returns 0 on success
+ */
+int main() {
+    int cmd = 0, key = 0;
+    std::cout << "Enter the initial size of Hash Table. = ";
+    std::cin >> totalSize;
+    table = std::vector<Entry>(totalSize);
+    bool loop = true;
+    while (loop) {
+        std::cout << std::endl;
+        std::cout << "PLEASE CHOOSE -" << std::endl;
+        std::cout << "1. Add key. (Numeric only)" << std::endl;
+        std::cout << "2. Remove key." << std::endl;
+        std::cout << "3. Find key." << std::endl;
+        std::cout << "4. Generate Hash. (Numeric only)" << std::endl;
+        std::cout << "5. Display Hash table." << std::endl;
+        std::cout << "6. Exit." << std::endl;
+        std::cin >> cmd;
+        switch (cmd) {
+            case 1:
+                std::cout << "Enter key to add = ";
+                std::cin >> key;
+                linear_probing::addInfo(key);
+                break;
+            case 2:
+                std::cout << "Enter key to remove = ";
+                std::cin >> key;
+                linear_probing::removalInfo(key);
+                break;
+            case 3: {
+                std::cout << "Enter key to search = ";
+                std::cin >> key;
+                Entry entry = table[linear_probing::linearProbe(key, true)];
+                if (entry.key == linear_probing::notPresent) {
+                    std::cout << "Key not present";
+                }
+                break;
+            }
+            case 4:
+                std::cout << "Enter element to generate hash = ";
+                std::cin >> key;
+                std::cout << "Hash of " << key
+                          << " is = " << linear_probing::hashFxn(key);
+                break;
+            case 5:
+                linear_probing::display();
+                break;
+            default:
+                loop = false;
+                break;
+                // delete[] table;
+        }
+        std::cout << std::endl;
+    }
+    return 0;
+}