LintCode 1227: Repeated Substring Pattern_repeated substring pattern lintcode-优快云博客

本文介绍了一种检测字符串是否由其子串重复拼接而成的算法。通过遍历可能的子串长度，检查原字符串是否能完全由该子串复制构成。此方法适用于字符串长度不超过10000的场景。

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Repeated Substring Pattern
Given a non-empty string check if it can be constructed by taking a substring of it and appending multiple copies of the substring together. You may assume the given string consists of lowercase English letters only and its length will not exceed 10000.

Example 1:

Input: “abab”

Output: True

Explanation: It’s the substring “ab” twice.
Example 2:

Input: “aba”

Output: False
Example 3:

Input: “abcabcabcabc”

Output: True

Explanation: It’s the substring “abc” four times. (And the substring “abcabc” twice.)

思路：取pattern size从1到len/2，然后原字符串分段与pattern比较。代码如下。注意去掉不可能的情况，这样可以节省时间。

class Solution {
public:
    /**
     * @param s: a string
     * @return: return a boolean
     */
    bool repeatedSubstringPattern(string &s) {
        int len = s.size();
        if (len & 0x1) return false;
        int halfLen = len >> 1;
        for (int i = 1; i <= halfLen; ++i) {
            string seg = s.substr(0, i);
            if (len % i != 0) continue;    //去掉不可能的情况
            int multi = len / i;
            bool isRepeated = true;
            for (int j = 0; j < multi; ++j) {
                if (s.substr(j * i, i) != seg) {
                    isRepeated = false;
                    break;
                }
            } 
            if (isRepeated) return true;
        }
        return false;
    } 
};