Repeated Substring Pattern

include/s0459_repeated_substring_pattern.hpp

@@ -0,0 +1,14 @@
+#ifndef S0459_REPEATED_SUBSTRING_PATTERN_HPP
+#define S0459_REPEATED_SUBSTRING_PATTERN_HPP
+
+#include <string>
+
+using namespace std;
+
+class S0459 {
+ public:
+  bool repeatedSubstringPattern(string s);
+  void getNext(string &s, int *next);
+};
+
+#endif

notes/src/SUMMARY.md

@@ -12,6 +12,7 @@
 - [翻转字符串里的单词](./reverse_words_in_a_string.md)
 - [左旋转字符串](./reverse_left_words.md)
 - [KMP](./kmp.md)
+- [重复的子字符串](./repeated_substring_pattern.md)
 
 # 经典代码
 

notes/src/repeated_substring_pattern.md

@@ -0,0 +1,23 @@
+# 重复的子字符串
+
+[459. Repeated Substring Pattern](https://leetcode.com/problems/repeated-substring-pattern/)
+
+给定一个非空的字符串，判断它是否可以由它的一个子串重复多次构成。给定的字符串只含有小写英文字母，并且长度不超过10000。
+
+示例:
+
+输入: "abab"
+
+输出: True
+
+解释: 可由子字符串 "ab" 重复两次构成。
+
+## 方法一
+
+将两个 s 拼接在一起，如果里面还出现一个 s 的话，就认为是由重复字符串构成的。
+
+## 方法二
+
+假设 s 是由 n 个 x 构成的，那么它的最长公共前后缀的长度是 `(n - 1) * len(x)` 。
+
+也就是说 `len(s) % (len(s) - (n - 1) * len(x)) == 0`

src/s0459_repeated_substring_pattern.cpp

@@ -0,0 +1,32 @@
+#include "s0459_repeated_substring_pattern.hpp"
+
+void S0459::getNext(string &s, int *next) {
+  int j{0};
+  int len = s.size();
+  next[0] = 0;
+  for (int i{1}; i < len; ++i) {
+    while (j > 0 && s[i] != s[j]) {
+      j = next[j - 1];
+    }
+    if (s[i] == s[j]) {
+      ++j;
+    }
+    next[i] = j;
+  }
+}
+
+bool S0459::repeatedSubstringPattern(string s) {
+  int len = s.size();
+  if (len <= 1) {
+    return false;
+  }
+  int next[len];
+  getNext(s, next);
+  if (next[len - 1] == 0) {
+    return false;
+  } else if (len % (len - next[len - 1]) == 0) {
+    return true;
+  } else {
+    return false;
+  }
+}

tests/s0459_repeated_substring_pattern.cpp

@@ -0,0 +1,31 @@
+#include "s0459_repeated_substring_pattern.hpp"
+
+#include <gtest/gtest.h>
+
+TEST(Problem459, Case1) {
+  string s{"abab"};
+  bool expected{true};
+  S0459 solution;
+  EXPECT_EQ(solution.repeatedSubstringPattern(s), expected);
+}
+
+TEST(Problem459, Case2) {
+  string s{"aba"};
+  bool expected{false};
+  S0459 solution;
+  EXPECT_EQ(solution.repeatedSubstringPattern(s), expected);
+}
+
+TEST(Problem459, Case3) {
+  string s{"abcabcabcabc"};
+  bool expected{true};
+  S0459 solution;
+  EXPECT_EQ(solution.repeatedSubstringPattern(s), expected);
+}
+
+TEST(Problem459, Case4) {
+  string s{"abac"};
+  bool expected{false};
+  S0459 solution;
+  EXPECT_EQ(solution.repeatedSubstringPattern(s), expected);
+}