Merge pull request #7 from colorbox/125

125. Valid Palindrome

Author: colorbox

125/1.cpp

@@ -0,0 +1,38 @@
+// 第1段階のコード
+class Solution {
+public:
+
+    template<class ForwardIt, class UnaryPredicate>
+    ForwardIt remove_if(ForwardIt first, ForwardIt last, UnaryPredicate p) {
+        ForwardIt filteredLast = first;
+        while (first != last) {
+            if (!p(*first)) {
+                *filteredLast = *first;
+                filteredLast++;
+            }
+            first++;
+        }
+
+        return filteredLast;
+    }
+    
+    bool isPalindrome(string s) {
+        string checker = s;
+        checker.erase(
+            remove_if(checker.begin(), checker.end(), [](unsigned char c) { return !isalnum(c); } ),
+            checker.end()
+        );
+
+        for (int i=0; i < checker.size(); i++) {
+            checker[i] = tolower(checker[i]);
+        }
+
+        string checkerReverse = checker;
+
+        reverse(checkerReverse.begin(), checkerReverse.end());
+
+        cout << checker << endl << checkerReverse << endl;
+
+        return (checker == checkerReverse);
+    }
+};

125/2.cpp

@@ -0,0 +1,19 @@
+// 第2段階のコード、第1段階のコードを読みやすくした
+class Solution {
+public:
+    bool isPalindrome(string s) {
+        string checker;
+
+        for (char c: s) {
+            if (isalnum(c)) {
+                checker += tolower(c);
+            }
+        }
+
+        string checkerReverse = checker;
+
+        reverse(checkerReverse.begin(), checkerReverse.end());
+
+        return (checker == checkerReverse);
+    }
+};

125/3.cpp

@@ -0,0 +1,19 @@
+// 第2段階のコード、3回連続でパスしたもの
+class Solution {
+public:
+    bool isPalindrome(string s) {
+        if (s.empty()) abort();
+
+        string checker;
+        for (char c: s) {
+            if (isalnum(c)) {
+                checker += tolower(c);
+            }
+        }
+
+        string reversedChecker = checker;
+        reverse(reversedChecker.begin(), reversedChecker.end());
+
+        return reversedChecker == checker;
+    }
+};

125/4.cpp

@@ -0,0 +1,29 @@
+// 3重ループを1重ループとしたコード
+class Solution {
+public:
+    bool isPalindrome(string s) {
+        if (s.empty()) abort();
+        int left = 0, right = s.size()-1;
+
+        while (left < right) {
+            if (!isalnum(s[left])) {
+                left++;
+                continue;
+            }
+
+            if (!isalnum(s[right])) {
+                right--;
+                continue;
+            }
+
+            if (tolower(s[left]) != tolower(s[right])) {
+                return false;
+            }
+
+            left++;
+            right--;
+        }
+
+        return true;
+    }
+};