chore(CPlusPlus): trie datastructure for searching added (#578)

algorithms/CPlusPlus/README.md

@@ -126,6 +126,10 @@
 - [Binary Tree Implementation](Trees/binary-tree-implementation.cpp)
 - [Iterative Segment Tree](Trees/IterativeSegmentTree.cpp)
 
+## Trie
+
+- [Trie for searching](Trie/trie_search.cpp)
+
 # Maths
 
 - [Kaprekar Number](Maths/Kaprekar-number.cpp)

algorithms/CPlusPlus/Trie/trie_search.cpp

@@ -0,0 +1,118 @@
+
+
+/*
+Trie is ds implementation of tree with one root and further 26 children at each layer and specifying if 
+it is end of tree. Better then hashmap in cases where we need to find words with same prefix,collisions 
+etc and used for word search spell check.
+
+*/
+
+#include <bits/stdc++.h>
+
+using namespace std;
+
+struct TrieNode *root;
+struct TrieNode
+{
+
+    struct TrieNode *children[26];
+
+    bool isEnd;
+};
+
+struct TrieNode *getNode()
+{
+
+    struct TrieNode *pNode = new TrieNode;
+    pNode->isEnd = false;
+    for (int i = 0; i < 26; i++)
+    {
+
+        pNode->children[i] = NULL;
+    }
+
+    return pNode;
+}
+class Trie
+{
+public:
+    /** Initialize your data structure here. */
+    TrieNode *root;
+    Trie()
+    {
+
+        root = new TrieNode();
+    }
+
+    /** Inserts a word into the trie. */
+    void insert(string word)
+    {
+
+        struct TrieNode *pcrawl = root;
+        for (int i = 0; i < word.length(); i++)
+        {
+
+            if (!pcrawl->children[word[i] - 'a'])
+                pcrawl->children[word[i] - 'a'] = getNode();
+
+            pcrawl = pcrawl->children[word[i] - 'a'];
+        }
+
+        pcrawl->isEnd = true;
+    }
+
+    /** Returns if the word is in the trie. */
+    bool search(string word)
+    {
+        struct TrieNode *pcrawl = root;
+        for (int i = 0; i < word.length(); i++)
+        {
+
+            if (!pcrawl->children[word[i] - 'a'])
+                return false;
+
+            pcrawl = pcrawl->children[word[i] - 'a'];
+        }
+
+        return pcrawl->isEnd;
+    }
+};
+
+int main()
+{
+
+    string keys[] = {"the", "a", "there",
+                     "answer", "any", "by",
+                     "bye", "their", "where", "when"};
+    int n = sizeof(keys) / sizeof(keys[0]);
+
+    Trie t;
+    t.root = getNode();
+    // Construct trie
+    for (int i = 0; i < n; i++)
+    {
+        t.insert(keys[i]);
+    }
+
+    // Search for different keys
+    cout << "'them' present in keys:";
+    t.search("them") ? cout << "Yes\n" : cout << "No\n";
+    cout << "'when' present in keys:";
+    t.search("when") ? cout << "Yes\n" : cout << "No\n";
+    return 0;
+}
+
+/*
+
+Time Complexity-
+O(key_length)
+Space Complexity-
+O(ALPHABET_SIZE * key_length * N), N is no. of keys in trie
+
+SAMPLE INPUT-OUTPUT
+
+'them' present in keys:No
+'when' present in keys:Yes
+
+
+*/