HDU1711 Number Sequence KMP

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题目传送门 - HDU1711

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题意概括

　　给T组数据，每组有长度为n和m的母串和模式串。判断模式串是否是母串的子串，如果是输出最先匹配完成的位置，否则输出-1.

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题解

　　KMP裸题。

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代码

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#include <cstring> #include <algorithm> #include <cstdio> #include <cstdlib> #include <cmath> using namespace std; const int N=1000005,M=10005; bool isd(char ch){     return '0'<=ch&&ch<='9'; } void read(int &x){     int f=1;     x=0;     char ch=getchar();     while (!isd(ch)&&ch!='-')         ch=getchar();     if (ch=='-')         f=-1,ch=getchar();     while (isd(ch))         x=x*10+ch-48,ch=getchar();     x*=f; } int T,n,m,a[N],b[M],Next[M]; int main(){     read(T);     while (T--){         read(n),read(m);         for (int i=0;i<n;i++)             read(a[i]);         for (int i=0;i<m;i++)             read(b[i]);         memset(Next,0,sizeof Next);         int k=0;         for (int i=1;i<m;i++){             while (k&&b[k]!=b[i])                 k=Next[k-1];             if (b[k]==b[i])                 k++;             Next[i]=k;         }         int ans=-1;         k=0;         for (int i=0;i<n;i++){             while (k&&b[k]!=a[i])                 k=Next[k-1];             if (b[k]==a[i])                 k++;             if (k==m){                 ans=i-m+2;                 break;             }         }         printf("%d\n",ans);     }     return 0; }