kmp算法实现

工作一直做web开发，今天偶尔看到讲解算法的blog，想试试看看根据思路能否自己实现下，对算法不自信的曾经的学渣同学竟然写出来了！正好好久不写blog，发一篇证明下自己还活着。

 

class kmp {
    
	final static boolean isDebug = false

	private static List getMatMapNumber(String str){
		def numList = [0]

		int len = str.size()
		str.eachWithIndex{ch, i ->
			// 首位是0，跳过
			if(i == 0)
				return

			numList[i] = 0

			String sub = str[0..i]
			List subPre = []
			List subSuf = []

			int lenSub = sub.size()
			for(j in 1..<lenSub){
				subPre << sub[0..<j]
				subSuf << sub[lenSub-j..-1]
			}

			if(isDebug){
				println 'For string - ' + sub
				println 'Pre - ' + subPre
				println 'Suf - ' + subSuf
			}

			String one = subPre.find{pre -> pre in subSuf}
			if(one)
				numList[i] = one.size()
		}

		numList
	}

	private static int findByMatInner(String str, String target, List numList, int beginSearch){
		int i = beginSearch, j = 0, len = target.size() 

		if(i >= str.size())
			return -1

		for(; j < len;){
			if(str[i] != target[j]){
				// 如果第一个就匹配不上，就下标 + 1，否则就下标移动的距离为“已经匹配的长度 - 最后匹配的字母对应的匹配数” 
				int stepForward = j == 0 ? 1 : j - numList[j - 1]
				println j + ' - ' + stepForward

				// 递归查找，移动开始匹配的下标
				return findByMatInner(str, target, numList, beginSearch + stepForward)
			}
			i++
			j++
		}

		return j == len ? i - len : -1
	}

	private static int findByMat(String str, String target){
		def numList = getMatMapNumber(target)
		findByMatInner(str, target, numList, 0)
	}

	static void main(String[] args){
		String str = 'bbc abcdab abcdabcdabde'
		String target = 'dabc'

//		println getMatMapNumber(target)

		int index = findByMat(str, target)
		println index
		println str[index..-1]
	}
}