LeetCode Tries Prefix Tree

 1 class TrieNode {

 2 public:

 3     const static int NR_FANOUT = 26;

 4     TrieNode* child[NR_FANOUT];

 5     int count;

 6     // Initialize your data structure here.

 7     TrieNode() {

 8         for (int i=0; i<NR_FANOUT; i++) {

 9             child[i] = NULL;

10         }

11         count = 0;

12     }

13 };

14 

15 class Trie {

16 public:

17     Trie() {

18         root = new TrieNode();

19     }

20 

21     // Inserts a word into the trie.

22     void insert(string s) {

23         insert(s, 0, root);

24     }

25 

26     // Returns if the word is in the trie.

27     bool search(string key) {

28         return search(key, 0, root) != NULL;

29     }

30 

31     // Returns if there is any word in the trie

32     // that starts with the given prefix.

33     bool startsWith(string prefix) {

34         return search_prefix(prefix, 0, root) != NULL;

35     }

36 private:

37     TrieNode* insert(string& s, int pos, TrieNode* current) {

38         int len = s.size();

39         if (pos > len) {

40             return NULL;

41         }

42         if (current == NULL) {

43             current = new TrieNode();

44         }

45         if (pos == len) {

46             current->count++;

47             return current;

48         }

49         int idx = s[pos] - 'a';

50         current->child[idx] = insert(s, pos + 1, current->child[idx]);

51         return current;

52     }

53 

54     TrieNode* search(string& s, int pos, TrieNode* current) {

55         if (current == NULL) {

56             return NULL;

57         }

58         int len = s.size();

59         if (pos > len) {

60             return NULL;

61         } else if (pos == len && current->count) {

62             return current;

63         }

64         return search(s, pos + 1, current->child[s[pos] - 'a']);

65     }

66     TrieNode* search_prefix(string& s, int pos, TrieNode* current) {

67         if (current == NULL) {

68             return NULL;

69         }

70         int len = s.size();

71         if (pos >= len) {

72             return current;

73         }

74         return search_prefix(s, pos + 1, current->child[s[pos] - 'a']);

75     }

76 private:

77     TrieNode* root;

78 };

mplement a trie with  insert ,  search , and  startsWith  methods.
Note:You may assume that all inputs are consist of lowercase letters  a-z .