49. Group Anagrams

49/step1.cpp

@@ -0,0 +1,22 @@
+/*
+Time: 7:07
+
+Time: O(N * M log M)
+Space: O(N * M)
+*/
+class Solution {
+public:
+    vector<vector<string>> groupAnagrams(vector<string>& strs) {
+        map<string, vector<string>> sorted_to_str;
+        for (auto str: strs) {
+          string key = str;
+          sort(key.begin(), key.end());
+          sorted_to_str[key].push_back(str);
+        }
+        vector<vector<string>>grouped_anagrams;
+        for (auto [key, group]: sorted_to_str) {
+          grouped_anagrams.push_back(group);
+        }
+        return grouped_anagrams;
+    }
+};

49/step2.cpp

@@ -0,0 +1,19 @@
+/*
+無駄なコピーをなくして空間計算量を改善。
+*/
+class Solution {
+public:
+    vector<vector<string>> groupAnagrams(vector<string>& strs) {
+        map<string, vector<string>> sorted_to_str;
+        for (auto& str: strs) {
+          string key = str;
+          sort(key.begin(), key.end());
+          sorted_to_str[key].push_back(str);
+        }
+        vector<vector<string>>grouped_anagrams;
+        for (auto& [key, group]: sorted_to_str) {
+          grouped_anagrams.push_back(move(group));
+        }
+        return grouped_anagrams;
+    }
+};

49/step2_2.cpp

@@ -0,0 +1,21 @@
+/*
+sortを利用せずに時間計算量を改善
+*/
+class Solution {
+public:
+    vector<vector<string>> groupAnagrams(vector<string>& strs) {
+        map<vector<int>, vector<string>> sorted_to_str;
+        for (auto& str: strs) {
+          vector<int> keys(26);
+          for (char c : str) {
+            keys[c - 'a']++;
+          }
+          sorted_to_str[keys].push_back(str);
+        }
+        vector<vector<string>>grouped_anagrams;
+        for (auto& [key, group]: sorted_to_str) {
+          grouped_anagrams.push_back(move(group));
+        }
+        return grouped_anagrams;
+    }
+};

49/step2_3.cpp

@@ -0,0 +1,26 @@
+/*
+文字列構築にstd::ostringstreamを使う
+*/
+class Solution {
+public:
+    vector<vector<string>> groupAnagrams(vector<string>& strs) {
+        map<string, vector<string>> sorted_to_str;
+        for (auto& str: strs) {
+          vector<int> counter(26);
+          for (char c : str) {
+            counter[c - 'a']++;
+          }
+          std::ostringstream key;
+          for (auto& count : counter) {
+            key << "#" << to_string(count);
+          }
+
+          sorted_to_str[key.str()].push_back(str);
+        }
+        vector<vector<string>>grouped_anagrams;
+        for (auto& [key, group]: sorted_to_str) {
+          grouped_anagrams.push_back(move(group));
+        }
+        return grouped_anagrams;
+    }
+};

49/step3.cpp

@@ -0,0 +1,16 @@
+class Solution {
+public:
+  vector<vector<string>> groupAnagrams(vector<string>& strs) {
+    map<string, vector<string>> sorted_to_strings;
+    for (auto& str : strs) {
+      string key = str;
+      sort(key.begin(), key.end());
+      sorted_to_strings[key].push_back(str);
+    }
+    vector<vector<string>> grouped_anagrams;
+    for (auto& [key, strings] : sorted_to_strings) {
+      grouped_anagrams.push_back(move(strings));
+    }
+    return grouped_anagrams;
+  }
+};