# KMP Algorithm Summary

Source: Internet
Author: User

Source: http://blog.csdn.net/qq_34494458/article/details/75253466

KMP algorithm, which is a pattern matching algorithm proposed by Knuth,morris,pratt, is a very good pattern matching algorithm for any pattern and target sequence, it can complete matching search in linear time without degradation.

`/** next[] Meaning (premise): x[i-next[i]...i-1] = X[0...next[i]-1] This is important, * next[i] to meet the maximum value of x[i-z...i-1] = X[0...z-1] Z (is the self-matching of x); /c1>*/  //the code implementation of next /** next[] [next[m], this next[m] role is still very large;*/voidKmp_pre (CharX[],intMintnext[]) {    intI, J; J= next[0] = -1; I=0;  while(I <m) { while(-1! = J && X[i]! = x[j]) j =Next[j]; //j =-1, indicating that the No. 0 digit did not match successfully; it is necessary to advance one directly;Next[++i] = + +K; }}/** There can also be a small optimization;*/voidPREKMP (CharX[],intMintkmpnext[]) {    intI, J; J= kmpnext[0] = -1; I=0;  while(I <m) { while(-1! = J && X[i]! = x[j]) j =Kmpnext[j]; if(X[++i] = = X[++j]) Kmpnext[i] =Kmpnext[j]; ElseKmpnext[i] =J; /*this if is 6, which removes some meaningless next[], presumably meaning * if the x[j] match fails, then execute j = next[j];        * and x[j] = x[next[j]] [so x[next[j]] will certainly match the failure.        * So it is meaningless to say this next[j]. */    }}/**x and y match; * Returns the number of occurrences of x in Y, which can overlap * and the next[] function is basically similar to the wording;*/  intnext[10010]; intKmp_count (CharX[],intMCharY[],intN) {//x is the pattern string, and Y is the main string;     intI, J; intAns =0; //PREKMP (x, M, next);kmp_pre (x, M, next); I= j =0;  while(I <N) { while(-1! = J && Y[i]! = x[j]) j =Next[j]; I++; J + +; if(J >=m) {ans++; J=Next[j]; }     }     returnans;}`

Classic topics:

Read his blog: http://blog.csdn.net/guhaiteng/article/details/52108690 plus a title: http://poj.org/problem?id=3167
`/** Pattern string can be floating pattern string matching problem * Given the relative size of the pattern string, need to find out the pattern string match number and position * such as pattern string: 1,4,4,2,3,1 and Main string: 5,6,2,10,10,7,3,2,9 * Then substring: 2,10,10,7,3, 2 is matched to the pattern string. * Idea: Just compare the number of the number with the current number is smaller than the current number is good, see whether these two things are equal to carry out KMP. */ //#include <bits/stdc++.h>#include <iostream>#include<string>#include<queue>#include<map>#include<cstring>#include<cstdio>#include<vector>using namespaceStd;typedefLong LongLL;#defineLson K<<1, LL, mid#defineRson k<<1|1, mid+1, RRConst intMAXN =100008;intN, K, S, next[maxn>>2], as[MAXN] [ -], bs[maxn>>2][ -], A[MAXN], B[maxn];vector<int>ans;voidInit () {//assimilation of input strings into as and BS;scanf"%d%d%d", &n, &k, &s);  for(inti =0; I < n; i++) {scanf ("%d", &A[i]); if(I! =0) {             for(intj =1; J < -; J + +)                 asI [j] = as[I1][j]; }         asI [a[i]]++; }     for(inti =0; I < K; i++) {scanf ("%d", &B[i]); if(I! =0) {             for(intj =1; J < -; J + +) Bs[i][j]= bs[i-1][j]; } Bs[i][b[i]]++; }}//here is the same way of writing without nested while loops. voidBuild_next () {next[0] = -1; next[1] =0;//There's a skin here.    intj =0, i =1;  while(I <k) {intT11 =0, T12, t21 =0, t22;  for(intt =1; T < B[i]; t++)            if(i = = j) T11 + =Bs[i][t]; ElseT11 + = (bs[i][t]-bs[i-j-1][t]); if(i = = j) T12 =Bs[i][b[i]]; ElseT12 = bs[i][b[i]]-bs[i-j-1][b[i]];  for(intt =1; T < B[j]; t++) t21+=Bs[j][t]; T22=Bs[j][b[j]]; if(T11 = = T21 && T12 = =t22) next[++i] = + +J; Elsej =Next[j]; }}voidKMP () {ans.clear ();    Build_next (); inti =0, j =0;  while(I <N) {intT11 =0, T12, t21 =0, t22;  for(intt =1; T < A[i]; t++)            if(i = = j) T11 + = as[i][t]; ElseT11 + = ( asI [t]- as[i-j-1][t]); if(i = = j) T12 = as[I][a[i]]; ElseT12 = asI [a[i]]- as[i-j-1][a[i]];  for(intt =1; T < B[j]; t++) t21+=Bs[j][t]; T22=Bs[j][b[j]]; if(T11 = = T21 && T12 = =t22) {            ++i; ++J; if(J >=k) {Ans.push_back (i-j+1); J=Next[j]; }        }        Elsej =Next[j]; }}intMain () {//freopen ("In.txt", "R", stdin);init ();    KMP (); printf ("%d\n", S =ans.size ());  for(inti =0; I < S; i++) printf ("%d\n", Ans[i]); return 0;}`

KMP Algorithm Summary

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