POJ-1472（循环复杂度，递归分治 + 多项式）

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题目：http://poj.org/problem?id=1472
思想是分而治之，核心是递归算法，重点是多项式乘法和加法
#include <cstdlib>#include <cstring>#include <iostream>#include <string>#include <vector>using namespace std;#define MAX     10class Polynomial{private:    struct Term{        int co, exp;        Term(int c, int e): co(c), exp(e){}    };    vector<Term> formula;//reverse of the normalized expression, each co > 0private:    void reset(int arr[MAX + 1]){        formula.clear();        for(int i = 0, n = MAX; i <= n; ++i){            if(arr[i]) formula.push_back(Term(arr[i], i));        }    }public:    Polynomial(){        formula.clear();    }    Polynomial(const string& s){        formula.clear();        if(s[0] == 'n') formula.push_back(Term(1, 1));        else if(int n = atoi(s.c_str())) formula.push_back(Term(n, 0));    }    Polynomial& operator *= (const Polynomial& other){        if(formula.empty()) return *this;        if(other.formula.empty()){            formula.clear();            return *this;        }                int arr[MAX + 1];        memset(arr, 0, sizeof(arr));        const vector<Term>& v = other.formula;        int i, n = v.size(), j, m = formula.size(), e, c;        for(i = 0; i < n; ++i){            e = v[i].exp;            c = v[i].co;            for(j = 0; j < m; ++j) arr[e + formula[j].exp] += c * formula[j].co;        }        reset(arr);        return *this;    }    Polynomial& operator += (const Polynomial& other){        if(other.formula.empty()) return *this;                int arr[MAX + 1];        memset(arr, 0, sizeof(arr));        const vector<Term>& v = other.formula;        int i, n;        for(i = 0, n = v.size(); i < n; ++i)            arr[v[i].exp] += v[i].co;        for(i = 0, n = formula.size(); i < n; ++i)            arr[formula[i].exp] += formula[i].co;        reset(arr);        return *this;    }    friend ostream& operator << (ostream& out, const Polynomial& poly){        const vector<Term>& formula = poly.formula;        if(formula.empty()){            out<< "0";            return out;        }        bool first = true;        for(int i = formula.size() - 1; i >= 0; --i){            if(first) first = false;            else out << "+";            if(formula[i].exp){                if(formula[i].co != 1) out << formula[i].co << "*";                out << "n";                if(formula[i].exp > 1) out << '^' << formula[i].exp;            }            else out << formula[i].co;        }        return out;    }};Polynomial analyseLoop(istream& in){    string s;    in >> s;    Polynomial poly(s), move;    while(in >> s, s != "END"){        if(s == "OP"){            in >> s;            move += Polynomial(s);        }        else move += analyseLoop(in);    }    return poly *= move;}Polynomial analyseProgram(istream& in){    string s;    Polynomial poly;    in >> s;    while(in >> s, s != "END"){        if(s == "LOOP") poly += analyseLoop(in);        else{            in >> s;            poly += Polynomial(s);        }    }    return poly;}int main(){    ios::sync_with_stdio(false);    int t, test;    cin >> test;    for(t = 1; t <= test; ++t){        cout << "Program #" << t << "\n";        cout << "Runtime = " << analyseProgram(cin) << "\n\n";    }    return 0;}
A了之后，感觉C++的函数重载特性简直酷毙了……
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