HASH求两子串是否相等(O(N)预处理O(1)比较)

来源：互联网发布：mac os x 10.12 beta5 编辑：程序博客网时间：2024/06/03 15:46

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>#include <string>using namespace std;const int MAXN = 5010;const unsigned long long SEED = 13331;unsigned long long P[MAXN];unsigned long long S[MAXN];unsigned long long RS[MAXN];string s;int n;unsigned long long HS( int l, int r ){//正向    if( l == r ){        return s[l];    }    l++;    r++;    return S[r] - S[l-1] * P[r-l+1];}unsigned long long RHS( int l, int r ){//反向    if( l == r ){        return s[l];    }    l = n - l - 1;    r = n - r - 1;    swap( l, r );    l++;    r++;    return RS[r] - RS[l-1] * P[r-l+1];}int main(){    cin >> s;    P[0] = 1;    for( int i = 1; i < MAXN; i++ ){        P[i] = P[i-1] * SEED;    }    n = s.size();    for( int i = 1; i <= n; i++ ){        S[i] = S[i-1] * SEED + s[i-1];    }    for( int i = 1; i <= n; i++ ){        RS[i] = RS[i-1] * SEED + s[n-i];    }    cout << (HS(0,3 ) == HS( 6,9 )) << endl;    return 0;}

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