常用数表和工具函数

阶乘表

//0-12的阶乘，unsigned int也只能表示到12!
const int factorial_13[13] = {1,1,2,6,24,120,720,5040,40320,362880,3628800,39916800,479001600};
//0-20的阶乘
const unsigned long long factorial_21[21] = {1,1,2,6,24,120,720,5040,40320,362880,3628800,39916800,479001600,6227020800,87178291200,1307674368000,20922789888000,355687428096000,6402373705728000,121645100408832000,2432902008176640000};

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组合数表

//0-20的组合数表，例如C[5][2]=10
const int C[21][21] = {
        {1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
        { 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
        { 1, 2, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
        { 1, 3, 3, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
        { 1, 4, 6, 4, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
        { 1, 5, 10, 10, 5, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
        { 1, 6, 15, 20, 15, 6, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
        { 1, 7, 21, 35, 35, 21, 7, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
        { 1, 8, 28, 56, 70, 56, 28, 8, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
        { 1, 9, 36, 84, 126, 126, 84, 36, 9, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
        { 1, 10, 45, 120, 210, 252, 210, 120, 45, 10, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
        { 1, 11, 55, 165, 330, 462, 462, 330, 165, 55, 11, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
        { 1, 12, 66, 220, 495, 792, 924, 792, 495, 220, 66, 12, 1, 0, 0, 0, 0, 0, 0, 0, 0 },
        { 1, 13, 78, 286, 715, 1287, 1716, 1716, 1287, 715, 286, 78, 13, 1, 0, 0, 0, 0, 0, 0, 0 },
        { 1, 14, 91, 364, 1001, 2002, 3003, 3432, 3003, 2002, 1001, 364, 91, 14, 1, 0, 0, 0, 0, 0, 0 },
        { 1, 15, 105, 455, 1365, 3003, 5005, 6435, 6435, 5005, 3003, 1365, 455, 105, 15, 1, 0, 0, 0, 0, 0 },
        { 1, 16, 120, 560, 1820, 4368, 8008, 11440, 12870, 11440, 8008, 4368, 1820, 560, 120, 16, 1, 0, 0, 0, 0 },
        { 1, 17, 136, 680, 2380, 6188, 12376, 19448, 24310, 24310, 19448, 12376, 6188, 2380, 680, 136, 17, 1, 0, 0, 0 },
        { 1, 18, 153, 816, 3060, 8568, 18564, 31824, 43758, 48620, 43758, 31824, 18564, 8568, 3060, 816, 153, 18, 1, 0, 0 },
        { 1, 19, 171, 969, 3876, 11628, 27132, 50388, 75582, 92378, 92378, 75582, 50388, 27132, 11628, 3876, 969, 171, 19, 1, 0 },
        { 1, 20, 190, 1140, 4845, 15504, 38760, 77520, 125970, 167960, 184756, 167960, 125970, 77520, 38760, 15504, 4845, 1140, 190, 20, 1 }
};

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斐波那契数表

const int fibonacci[31]={0,1,1,2,3,5,8,13,21,34,55,89,144,233,377,610,987,1597,2584,4181,6765,10946,17711,28657,46368,75025,121393,196418,317811,514229,832040};

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素数筛

使用素数筛对素数进行打表：

//将小于n的素数打表
vector<char> table_prime(int n) {
    if (n <= 2) {
        return {0, 0};
    }
    vector<char> res(n, 1);
    res[0] = res[1] = 0;
    for (int i = 2; i < n; ++i) {
        if (res[i] == 1) {
            for (int j = i * 2; j < n; j += i) {
                res[j] = 0;
            }
        }
    }
    return res;
}

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从字符串中提取单词

vector<string> participle_words(string paragraph) {
    vector<string> res;
    string s = "";
    bool flag = false;
    for (auto c : paragraph) {
        if (isalpha(c)) {
            if (flag) {
                if (s != "") {
                    res.push_back(s);
                }
                s = "";
                flag = false;
            }
            s += c;
        } else {
            flag = true;
        }
    }
    if (s != "") {
        res.push_back(s);
    }
    return res;
}