KMP算法

标签：

如果match的长度大于str长度(M>N)，str必然不会含有match，可直接返回-1。但如果N>=M，要求算法复杂度O(N)。 

   public int getIndexOf(String s, String m) { 
        if (s == null || m == null || m.length() < 1 || s.length() < m.length()) { 
        return -1; 
        } 
        char[] ss = s.toCharArray(); 
        char[] ms = m.toCharArray(); 
        int si = 0; 
        int mi = 0; 
        int[] next = getNextArray(ms); 
        while (si < ss.length && mi < ms.length) { 
        if (ss[si] == ms[mi]) { 
            si++; 
            mi++; 
        } else if (next[mi] == -1) { 
            si++; 
        } else { 
            mi = next[mi]; 
        } 
        } 
        return mi == ms.length ? si - mi : -1; 
    } 


    public int[] getNextArray(char[] ms) { 
        if (ms.length == 1) { 
            return new int[] { -1 }; 
        } 
        int[] next = new int[ms.length]; 
        next[0] = -1; 
        next[1] = 0; 
        int pos = 2; 
        int cn = 0; 
        while (pos < next.length) { 
            if (ms[pos - 1] == ms[cn]) { 
                next[pos++] = ++cn; 
            } else if (cn > 0) { 
                cn = next[cn]; 
            } else { 
                next[pos++] = 0; 
            } 
        } 
        return next; 
    }

KMP算法

标签：

原文地址：http://blog.csdn.net/wangfengfan1/article/details/47843045