class Solution {
    public String reverseWords(String s) {
        String ans = "";
        int start = -1, end = -1;
        for (int i = s.length() - 1; i>=0; i--){
            if(s.charAt(i) != ' ' && end == -1){
                end = i;
            }
            else if(s.charAt(i) == ' ' && end != -1){
                start = i + 1;
                ans = ans + s.substring(start, end+1) + " ";
                start = -1;
                end =-1;
            }
            if(i == 0 && end != -1){
                ans = ans + s.substring(i, end+1);
            }
        }
        return ans.trim();
    }
}

class Solution {
    public int strStr(String haystack, String needle) {
        if (needle.length() == 0) return 0;
        int[] next = new int[needle.length()];
        getNext(next, needle);

        int j = 0;
        for (int i = 0; i < haystack.length(); i++) {
            while (j > 0 && needle.charAt(j) != haystack.charAt(i)) 
                j = next[j - 1];
            if (needle.charAt(j) == haystack.charAt(i)) 
                j++;
            if (j == needle.length()) 
                return i - needle.length() + 1;
        }
        return -1;

    }
    
    private void getNext(int[] next, String s) {
        int j = 0;
        next[0] = 0;
        for (int i = 1; i < s.length(); i++) {
            while (j > 0 && s.charAt(j) != s.charAt(i)) 
                j = next[j - 1];
            if (s.charAt(j) == s.charAt(i)) 
                j++;
            next[i] = j; 
        }
    }
}

public boolean repeatedSubstringPattern(String str) {
	int l = str.length();
	for(int i=l/2;i>=1;i--) {
		if(l%i==0) {
			int m = l/i;
			String subS = str.substring(0,i);
			StringBuilder sb = new StringBuilder();
			for(int j=0;j<m;j++) {
				sb.append(subS);
			}
			if(sb.toString().equals(str)) return true;
		}
	}
	return false;
}

class Solution {
    public boolean repeatedSubstringPattern(String s) {
        if (s.equals("")) return false;

        int len = s.length();
        // 原串加个空格(哨兵)，使下标从1开始，这样j从0开始，也不用初始化了
        s = " " + s;
        char[] chars = s.toCharArray();
        int[] next = new int[len + 1];

        // 构造 next 数组过程，j从0开始(空格)，i从2开始
        for (int i = 2, j = 0; i <= len; i++) {
            // 匹配不成功，j回到前一位置 next 数组所对应的值
            while (j > 0 && chars[i] != chars[j + 1]) j = next[j];
            // 匹配成功，j往后移
            if (chars[i] == chars[j + 1]) j++;
            // 更新 next 数组的值
            next[i] = j;
        }

        // 最后判断是否是重复的子字符串，这里 next[len] 即代表next数组末尾的值
        if (next[len] > 0 && len % (len - next[len]) == 0) {
            return true;
        }
        return false;
    }
}