[code fix] Fixed trie_tree for code quality and docs & clang-tidy error check (#1059)

* attempt to fix trie-tree code

* clang-tidy fixes

* remove performance-unnecessary-value-param as error - this has auto-fix

* make test() static

* added original author to the description

* added namespace

* doc updates

* fix true spelling

* extended to small & big caps alphabets - 52 characters

* clang-format and clang-tidy fixes for edc2247a

* move const parameter to after the parameters
Co-authored-by: Ngithub-actions <${GITHUB_ACTOR}@users.noreply.github.com>

.clang-tidy

 ---
 Checks:          '-*,google-*,clang-analyzer-*,-clang-analyzer-security.insecureAPI.*,cppcoreguidelines-*,-cppcoreguidelines-avoid-magic-numbers,-cppcoreguidelines-pro-bounds-*,openmp-*,performance-*,portability-*,modernize-*,-modernize-use-trailing-*'
-WarningsAsErrors: '*,-google-readability-*,-google-explicit-constructor,-modernize-*,modernize-avoid-c-arrays,-performance-move-const-arg,-performance-noexcept-move-constructor,-cppcoreguidelines-init-variables,-cppcoreguidelines-pro-*,-cppcoreguidelines-owning-memory,-clang-analyzer-cplusplus.Move'
+WarningsAsErrors: '*,-google-readability-*,-google-explicit-constructor,-modernize-*,modernize-avoid-c-arrays,-performance-move-const-arg,-performance-noexcept-move-constructor,-performance-unnecessary-value-param,-cppcoreguidelines-init-variables,-cppcoreguidelines-pro-*,-cppcoreguidelines-owning-memory,-clang-analyzer-cplusplus.Move'
 HeaderFilterRegex: ''
 AnalyzeTemporaryDtors: false
 FormatStyle:     '{ BasedOnStyle: Google, UseTab: Never, IndentWidth: 4, TabWidth: 4, AllowShortIfStatementsOnASingleLine: false, IndentCaseLabels: true, ColumnLimit: 80, AccessModifierOffset: -3, AlignConsecutiveMacros: true }'

data_structures/trie_tree.cpp

-#include <stdbool.h>
-#include <stdio.h>
-
+/**
+ * @file
+ * @author [@Arctic2333](https://github.com/Arctic2333)
+ * @author [Krishna Vedala](https://github.com/kvedala)
+ * @brief Implementation of [Trie](https://en.wikipedia.org/wiki/Trie) data
+ * structure for English alphabets in small characters.
+ * @note the function ::data_structure::trie::deleteString might be erroneous
+ * @see trie_modern.cpp
+ */
+#include <array>
+#include <cassert>
 #include <iostream>
+#include <memory>
 #include <string>
+#include <vector>
 
-// structure definition
-typedef struct trie {
-    struct trie* arr[26];
-    bool isEndofWord;
-} trie;
-
-// create a new node for trie
-trie* createNode() {
-    trie* nn = new trie();
-    for (int i = 0; i < 26; i++) nn->arr[i] = NULL;
-    nn->isEndofWord = false;
-    return nn;
-}
+/** \namespace data_structure
+ * \brief Data-structure algorithms
+ */
+namespace data_structure {
+/**
+ * @brief [Trie](https://en.wikipedia.org/wiki/Trie) implementation for
+ * small-case English alphabets `a-z`
+ */
+class trie {
+ private:
+    static constexpr uint8_t NUM_CHARS = 26;  ///< Number of alphabets
+    /** @brief Recursive tree nodes as an array of shared-pointers */
+    std::array<std::shared_ptr<trie>, NUM_CHARS << 1> arr;
+    bool isEndofWord = false;  ///< identifier if a node is terminal node
 
-// insert string into the trie
-void insert(trie* root, std::string str) {
-    for (int i = 0; i < str.length(); i++) {
-        int j = str[i] - 'a';
-        if (root->arr[j]) {
-            root = root->arr[j];
-        } else {
-            root->arr[j] = createNode();
-            root = root->arr[j];
+    /**
+     * @brief Convert a character to integer for indexing
+     *
+     * @param ch character to index
+     * @return unsigned integer index
+     */
+    uint8_t char_to_int(const char& ch) const {
+        if (ch >= 'A' && ch <= 'Z') {
+            return ch - 'A';
+        } else if (ch >= 'a' && ch <= 'z') {
+            return ch - 'a' + NUM_CHARS;
         }
+
+        std::cerr << "Invalid character present. Exiting...";
+        std::exit(EXIT_FAILURE);
+        return 0;
     }
-    root->isEndofWord = true;
-}
 
-// search a string exists inside the trie
-bool search(trie* root, std::string str, int index) {
-    if (index == str.length()) {
-        if (!root->isEndofWord)
+    /** search a string exists inside a given root trie
+     * @param str string to search for
+     * @param index start index to search from
+     * @returns `tre` if found
+     * @returns `false` if not found
+     */
+    bool search(const std::shared_ptr<trie>& root, const std::string& str,
+                int index) {
+        if (index == str.length()) {
+            if (!root->isEndofWord) {
+                return false;
+            }
+            return true;
+        }
+        int j = char_to_int(str[index]);
+        if (!root->arr[j]) {
             return false;
-        return true;
+        }
+        return search(root->arr[j], str, index + 1);
     }
-    int j = str[index] - 'a';
-    if (!root->arr[j])
-        return false;
-    return search(root->arr[j], str, index + 1);
-}
 
-/*
-removes the string if it is not a prefix of any  other
-string, if it is then just sets the endofword to false, else
-removes the given string
-*/
-bool deleteString(trie* root, std::string str, int index) {
-    if (index == str.length()) {
-        if (!root->isEndofWord)
-            return false;
-        root->isEndofWord = false;
-        for (int i = 0; i < 26; i++) return false;
-        return true;
+ public:
+    trie() = default;  ///< Class default constructor
+
+    /** insert string into the trie
+     * @param str String to insert in the tree
+     */
+    void insert(const std::string& str) {
+        std::shared_ptr<trie> root(nullptr);
+
+        for (const char& ch : str) {
+            int j = char_to_int(ch);
+            if (root) {
+                if (root->arr[j]) {
+                    root = root->arr[j];
+                } else {
+                    std::shared_ptr<trie> temp(new trie());
+                    root->arr[j] = temp;
+                    root = temp;
+                }
+            } else if (arr[j]) {
+                root = arr[j];
+            } else {
+                std::shared_ptr<trie> temp(new trie());
+                arr[j] = temp;
+                root = temp;
+            }
+        }
+        root->isEndofWord = true;
     }
-    int j = str[index] - 'a';
-    if (!root->arr[j])
-        return false;
-    bool var = deleteString(root, str, index + 1);
-    if (var) {
-        root->arr[j] = NULL;
-        if (root->isEndofWord) {
+
+    /** search a string exists inside the trie
+     * @param str string to search for
+     * @param index start index to search from
+     * @returns `true` if found
+     * @returns `false` if not found
+     */
+    bool search(const std::string& str, int index) {
+        if (index == str.length()) {
+            if (!isEndofWord) {
+                return false;
+            }
+            return true;
+        }
+        int j = char_to_int(str[index]);
+        if (!arr[j]) {
             return false;
-        } else {
-            int i;
-            for (i = 0; i < 26; i++)
-                if (root->arr[i])
-                    return false;
+        }
+        return search(arr[j], str, index + 1);
+    }
+
+    /**
+     * removes the string if it is not a prefix of any  other
+     * string, if it is then just sets the ::data_structure::trie::isEndofWord
+     * to false, else removes the given string
+     * @note the function ::data_structure::trie::deleteString might be
+     * erroneous
+     * @todo review the function ::data_structure::trie::deleteString and the
+     * commented lines
+     * @param str string to remove
+     * @param index index to remove from
+     * @returns `true` if successful
+     * @returns `false` if unsuccessful
+     */
+    bool deleteString(const std::string& str, int index) {
+        if (index == str.length()) {
+            if (!isEndofWord) {
+                return false;
+            }
+            isEndofWord = false;
+            // following lines - possible source of error?
+            // for (int i = 0; i < NUM_CHARS; i++)
+            //     if (!arr[i])
+            //         return false;
             return true;
         }
+        int j = char_to_int(str[index]);
+        if (!arr[j]) {
+            return false;
+        }
+        bool var = deleteString(str, index + 1);
+        if (var) {
+            arr[j].reset();
+            if (isEndofWord) {
+                return false;
+            } else {
+                int i = 0;
+                for (i = 0; i < NUM_CHARS; i++) {
+                    if (arr[i]) {
+                        return false;
+                    }
+                }
+                return true;
+            }
+        }
+
+        /* should not return here */
+        std::cout << __func__ << ":" << __LINE__
+                  << "Should not reach this line\n";
+        return false;
     }
+};
+}  // namespace data_structure
+
+/**
+ * @brief Testing function
+ * @returns void
+ */
+static void test() {
+    data_structure::trie root;
+    root.insert("Hello");
+    root.insert("World");
+
+    assert(!root.search("hello", 0));
+    std::cout << "hello - " << root.search("hello", 0) << "\n";
+
+    assert(root.search("Hello", 0));
+    std::cout << "Hello - " << root.search("Hello", 0) << "\n";
 
-    /* should not return here */
-    std::cout << __func__ << ":" << __LINE__ << "Should not reach this line\n";
-    return false;
+    assert(!root.search("Word", 0));
+    std::cout << "Word - " << root.search("Word", 0) << "\n";
+
+    assert(root.search("World", 0));
+    std::cout << "World - " << root.search("World", 0) << "\n";
+
+    // Following lines of code give erroneous output
+    // root.deleteString("hello", 0);
+    // assert(!root.search("hello", 0));
+    // std::cout << "hello - " << root.search("world", 0) << "\n";
 }
 
+/**
+ * @brief Main function
+ * @return 0 on exit
+ */
 int main() {
-    trie* root = createNode();
-    insert(root, "hello");
-    insert(root, "world");
-    int a = search(root, "hello", 0);
-    int b = search(root, "word", 0);
-    printf("%d %d ", a, b);
+    test();
+
     return 0;
 }