KMP

    public int[] computePrefix(char[] p)
    {
    	int	i, n, k;
    	n = p.length;
    	int[] next = new int[n];
    	next[1] = next[0] = 0;
    	k = next[1];	
    	for (i = 2; i <= n - 1; i++) {
    		for (; k != 0 && p[k] != p[i-1]; k = next[k]);
    		if (p[k] == p[i-1]) k++;
    		next[i] = k;
    	}
    	return next;
    }
    
    public int contains(String src,String pattern){
    	int srcLength = src.length();
    	int patternLength = pattern.length();
    	int s = 0;
    	int p = 0;
    	int k = 0;
    	int[] next = computePrefix(pattern.toCharArray());
    	char[] srcChars = src.toCharArray();
    	char[] patternChars = pattern.toCharArray();
    	while(s < srcLength){
    		for(p = next[p];p < patternLength && srcChars[s] == patternChars[p];p ++ ,s ++);
    		if(p == 0){
    			s++;
    		}else if(p == patternLength){
    			return s - p;
    		}
    	}
    	return -1;
    }
    
    public static void main(String[] orgs) {
		KMP bf = new KMP();
		System.out.println(bf.contains("123123445233423", "4452"));
	}