17 621

Author: LuYanFCP

README.md

@@ -35,6 +35,7 @@ Leetcode刷题记录
 
 ### dfs/bfs
 
++ No.17 [cpp](cpp/17.cpp)
 + No.46 [python](python/46.py)
 + No.126 [cpp](cpp/126.cpp) [python](python/126.py)
 + No.543 [cpp](cpp/543.cpp) [python](python/543.py)
@@ -130,6 +131,7 @@ Leetcode刷题记录
 
 + No.1025 [python](python/1025.py)
 + No.149 [cpp](cpp/149.cpp)
++ No.621 [cpp](cpp/621.cpp)
 
 ## 剑指offer系列
 

cpp/17.cpp

@@ -0,0 +1,38 @@
+#include<bits/stdc++.h>
+
+using namespace std;
+
+class Solution {
+public:
+    vector<string> letterCombinations(string digits) {
+        if (digits.size() == 0) return {};
+        unordered_map<char, vector<char>> hash_map = {
+            {'2', {'a', 'b', 'c'}}, 
+            {'3', {'d', 'e', 'f'}},
+            {'4', {'g', 'h', 'i'}},
+            {'5', {'j', 'k', 'l'}},
+            {'6', {'m', 'n', 'o'}},
+            {'7', {'p', 'q', 'r', 's'}},
+            {'8', {'t', 'u', 'v'}},
+            {'9', {'w', 'x', 'y', 'z'}}
+        };
+        
+        vector<string> res;
+        vector<char> temp;
+        dfs(digits, 0, hash_map, temp, res);
+        return res;
+
+    }
+    void dfs(string &digits, int idx, unordered_map<char, vector<char>> &hash_map, vector<char> &temp,vector<string> &res)
+    {
+        int n = digits.size(), m = hash_map[digits[idx]].size();
+        if (idx == n)  
+            res.emplace_back(temp.begin(), temp.end());
+        
+        for (int i = 0; i < m; ++i) {
+            temp.push_back(hash_map[digits[idx]][i]);
+            dfs(digits, idx+1, hash_map, temp, res);
+            temp.pop_back();
+        }
+    }
+};