[Ybtoj High-efficiency Advanced 2.3] [kmp] Substring search

[Ybtoj High-efficiency Advanced 2.3] [kmp] Substring search

topic

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Problem-solving ideas

The strategy of kmp template question kmp is to adjust $k$ point position (decrease$k$ value) and make$The$ value of$k$ is as large as possible so that$A$[$i$-$j$+1…$i$]=$B$[1…$j$ ] Keep matching and try to match$A$[$i$ +1] Give$B$[$j$+1]

board

for (int i=1;i<=len1;i++)
	{
    
    
		while (k!=0&&x[i]!=y[k+1]) k=next[k];
		if (x[i]==y[k+1]) k++;
		if (k==len2) ans++;  
	}

Explanation of the manual push process
$P.S$ $next$ is$The$ string$B$ matches itself
is xx in the board$x$和$y$ ran out the same

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Code

#include<iostream> 
#include<cstring>
#include<cstdio>
using namespace std;
int len1,len2,ans;
int next[1000010]; 
char x[1000010],y[1000010];
int main()
{
    
    
	scanf("%s%s",x+1,y+1);
	len1=strlen(x+1); 
	len2=strlen(y+1);
	next[1]=0;
	int k=0;
	for (int i=2;i<=len2;i++)
	{
    
     
		while (k>0&&y[i]!=y[k+1]) k=next[k];
		if (y[i]==y[k+1]) k++;
		next[i]=k; 
	}  //B串自己匹配，求出next
	k=0;
	for (int i=1;i<=len1;i++)
	{
    
    
		while (k!=0&&x[i]!=y[k+1]) k=next[k];
		if (x[i]==y[k+1]) k++;
		if (k==len2) ans++;  //完全匹配，次数+1
	}  //A串和B串匹配
	printf("%d\n",ans);
	return 0;
}