KMP

/**
 * 时间复杂度，生成next数组是O(m)， 搜索是O(n)，整体是O(m+n).
 *
 */
public class KMP {

	public int find(char[] s, char[] t){
		assert(true);
		int[] next = getNextArray(t);
		int i = 0;
		int j = 0;
		while((i<s.length)){
			if(s[i] == t[j]){
				i++;
				j++;
				if(j == t.length){
					return i-j;
				}
			}else{
				j = next[j];
				if(j == -1){
					i++;
					j = 0;
				}
			}
		}
		return -1;
	}
	public int[] getNextArray(char[] t){
		assert(true);
		int[] next = new int[t.length];
		next[0] = -1;
		int i=0;
		while(i < t.length-1){
			next[i+1] = getNext(t, next, i, i);
			i++;
		}
		return next;
	}
	
	/**
	 * @param t 模式字符串
	 * @param next next数组
	 * @param pCurrent 当前待匹配位置
	 * @param p 已知next位置
	 * @return 下一个位置的值，next[p+1]
	 */
	private int getNext(char[] t, int[] next, int pCurrent, int p){
		int current = next[pCurrent];
		if(current == -1){
			return 0;
		}
		if(t[p] == t[current]){
			return current + 1;
		}else{
			return getNext(t, next, current, p);
		}
	}
	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		char[] s = "abababc".toCharArray();
		char[] t = "ababc".toCharArray();
		KMP kmp = new KMP();
		int p = kmp.find(s, t);
		System.out.println(p);
		
		Tools.printArray(kmp.getNextArray(t));
	}

}