POJ3461 HDU1686 SCU2652 Oulipo

題目連結 POJ
題目連結 HDU
題目連結 SCU

  • 題意：給定字串 W,T ，求 W 在 T 出現的次數。
  • 題解：利用 KMP 算出。
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    #pragma GCC optimize(2)
    #include <algorithm>
    #include <cmath>
    #include <cstring>
    #include <iostream>
    #include <map>
    #include <string>
    #include <vector>
    using namespace std;
    typedef unsigned long long ULL;
    const int INF = 1e9;
    const int MXN = 1e5 + 5;
    const int MXV = 3e5 + 5;
    const ULL MOD = 10009;
    const ULL seed = 31;
    #define MP make_pair
    #define PB push_back
    #define F first
    #define S second
    #define FOR(i, L, R) for (int i = L; i != (int)R; ++i)
    #define FORD(i, L, R) for (int i = L; i != (int)R; --i)
    #define IOS                                                                    \
        cin.tie(NULL);                                                             \
        cout.tie(NULL);                                                            \
        ios_base::sync_with_stdio(false);

    int fail[MXN];
    void bulid_fail_funtion(string B)
    {
        int len = B.length(), current_pos;
        current_pos = fail[0] = -1;
        for (int i = 1; i < len; i++)
        {
            while (current_pos != -1 && B[current_pos + 1] != B[i])
            {
                current_pos = fail[current_pos];
            }
            if (B[current_pos + 1] == B[i])
            {
                current_pos++;
            }
            fail[i] = current_pos;
        }
    }

    int match(string A, string B)
    {
        int lenA = A.size(), lenB = B.size();
        int current_pos = -1;
        int ans = 0;
        for (int i = 0; i < lenA; i++)
        {
            while (current_pos != -1 && B[current_pos + 1] != A[i])
            {
                current_pos = fail[current_pos];
            }
            if (B[current_pos + 1] == A[i])
                current_pos++;
            if (current_pos == lenB - 1)
            { // match! A[i-lenB+1,i]=B
                current_pos = fail[current_pos];
                ++ans;
            }
        }
        return ans;
    }
    int main()
    {
        IOS;
        int t;
        cin >> t;
        while (t--)
        {
            string s, r;
            cin >> s >> r;
            bulid_fail_funtion(s);
            cout << match(r, s) << '\n';
        }
    }

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