Add C++ solution of problem #2185

Author: Cuda-Chen

Diff for: 2185/solution.cpp

@@ -0,0 +1,51 @@
+// trie
+// trie implementation adopt from: https://walkccc.me/LeetCode/problems/3042/
+
+struct TrieNode {
+    unordered_map<char, shared_ptr<TrieNode>> c;
+    int cnt = 0;
+};
+
+class Trie {
+public:
+    void insert(const string &w) {
+        int cnt = 0;
+        shared_ptr<TrieNode> n = root;
+        for(char j : w) {
+            if(!n->c[j])
+                n->c[j] = make_shared<TrieNode>();
+            n = n->c[j];
+            n->cnt++;
+        }
+    }
+
+    int search(const string &w) {
+        shared_ptr<TrieNode> n = root;
+        if(!n->c[w[0]])
+            return 0;
+        n = n->c[w[0]];
+        int ans = n->cnt;
+        for(int i = 1; i < w.size(); i++) {
+            if(!n->c[w[i]])
+                return 0;
+            n = n->c[w[i]];
+            ans = min(ans, n->cnt);
+        }
+        return ans;
+    }
+
+private:
+    shared_ptr<TrieNode> root = make_shared<TrieNode>();
+};
+
+class Solution {
+public:
+    int prefixCount(vector<string>& words, string pref) {
+        Trie trie;
+
+        for(string w : words)
+            trie.insert(w);
+
+        return trie.search(pref);
+    }
+};