高精度计算模板

高精度计算

加

string add(string a,string b){
    if(a.size() > b.size()) swap(a,b);
    b.insert(b.begin(),'0');
    int t = 0;
    for(int i = b.size()-1,j = a.size()-1;i>=0;i--,j--){
        int cur;
        if(j>=0) cur = (a[j]-'0') + (b[i]-'0') + t;
        else cur = (b[i] - '0') +t;
        b[i] = (cur%10) + '0';
        t = cur/10;
    }
    int idx = b.find_first_not_of('0');
    return idx != -1? b.substr(idx): "0";
}

减

string sub(string a,string b){
    //a大b小
    int t = 0;
    for(int i = a.size()-1,j = b.size()-1;i>=0;i--,j--){
        int up = 0,down = 0;
        up = (a[i]-'0') + t; t = 0;
        if(j>=0) down = (b[j]-'0');
        if(up < down) up+=10,t = -1;
        int cur = up-down;
        a[i] = cur+'0';
    }
    int idx = a.find_first_not_of('0');
    return idx != -1? a.substr(idx) : "0";
}

乘（高精度*低精度）

string mul(string a,ll b){
    string c = "";
    ll t = 0;
    for(int i = a.size()-1;i>=0 || t;i--){
        if(i>=0) t += (a[i]-'0')*b;
        c += (t%10) +'0';
        t/=10;
    }
    reverse(c.begin(),c.end());
    return c;
}

除（高精度/低精度）

返回商的整数部分

string div(string a,ll b){
    string c = "";
    ll cur = 0;
    for(int i = 0;i<a.size();i++){
        cur = cur*10 + (a[i]-'0');
        c += to_string(cur/b);
        cur %= b;
    }
    int idx = c.find_first_not_of('0');
    return idx!=-1 ? c.substr(idx) : "0";
}

比较大小

bool cmp(string a,string b){
    int idx1 = a.find_first_not_of('0'),idx2 = b.find_first_not_of('0');
    a = idx1!=-1? a.substr(idx1) : "0";
    b = idx2!=-1? b.substr(idx2) : "0";
    if(a.size() != b.size()) return a.size() >= b.size();
    return a>=b;
}