刘汝佳算法竞赛入门经典 第二单元习题答案自编

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@2-1
#include <fstream>
using namespace std;

ifstream fin("aplusb.in");
ofstream fout("aplusb.out");
int main(){
    int n;
    while(fin>>n){
        int count = 0;
        //计算位数
        while(n){
            count++;
            n /= 10;
        }
        fout << count << endl;
    }
    return 0;
}


@2-2
#include <fstream>
using namespace std;

ifstream fin("aplusb.in");
ofstream fout("aplusb.out");
int main(){
    int n;
    for(int i = 100; i < 1000; i++){
        int A = i/100, B = i%100%10, C = i % 10;
        if(A*A*A+B*B*B+C*C*C == i)
            fout << i << "^_______________________________________________________^"<< endl;
        else fout << "it is not~" << endl;
    }
    return 0;
}


@2-3
#include <fstream>
using namespace std;

ifstream fin("aplusb.in");
ofstream fout("aplusb.out");
int main(){
    int a, b, c, i;
    while(fin >>a>>b>>c){
        for(i = 10; i <= 100; i++){
            if(i%3 == a && i%5==b && i%7==c){
                fout << i << endl;
                break;
            }
        }
        if(i == 101) fout << "No answer" << endl;
    }
    return 0;
}


@2-4
#include <fstream>
using namespace std;

ifstream fin("aplusb.in");
ofstream fout("aplusb.out");
int main(){
    int n;
    for(int i = 1; i <=5; i++){
        //输出空格0-4个
        for(int j = 1; j <= i-1; j++) fout << " ";
        //输出# 11-2i
        for(int k = 1; k <= 11-2*i; k++) fout << "#";
        fout << endl;
    }
    return 0;
}


@2-5
#include <fstream>
using namespace std;

ifstream fin("aplusb.in");
ofstream fout("aplusb.out");

int main(){
    int n;
    while(fin >> n){
        int a[n], m, i = 0, count = 0;
        while(i < n) fin >> a[i++];
        fin >> m;
        for(i = 0; i < n; i++){
            if(a[i] < m) count++;
        }
        fout << count << endl;
    }
    return 0;
}


@2-6
#include <fstream>
#include <iostream>
#include <iomanip>
using namespace std;

ifstream fin("aplusb.in");
ofstream fout("aplusb.out");

int main(){
    int n;
    while(fin >> n){
        double count = 0;
        int i = 1;
        while(i <= n) count += 1.0/i;
        fout << fixed<< setprecision(3) << count << endl;
    }
    return 0;
}


@2-7
#include <fstream>
#include <iostream>
#include <iomanip>
using namespace std;

ifstream fin("aplusb.in");
ofstream fout("aplusb.out");

int main(){
    double count = 0;
    int i = 1, flag = -1;

    while(1.0/i >= 1.0e-6){
        flag *= -1;//flag取反,使每一项变符号
        double temp = 1.0/i;
        count += flag * temp;
        i += 2;
    }
    fout << count << endl;
    return 0;
}


@2-8
#include <iostream>
#include <fstream>
#include <iomanip>
using namespace std;

ifstream fin("aplusb.in");
ofstream fout("aplusb.out");
int main(void){
    long long  n, m;
    while(fin >> n >> m){
        long long loop = n;
        double sum = 0.0;
        while(loop <= m){
            double add = 1.0/(loop*loop);
            sum += add;
            loop++;
        }
        fout << fixed << setprecision(5)<< sum << endl;
    }
    return 0;
}


@2-9
#include <iostream>
#include <fstream>
#include <iomanip>
using namespace std;
ifstream fin("aplusb.in");
ofstream fout("aplusb.out");
int main(void){
    int a, b, c;
    while(fin >> a >> b >> c){
        fout << fixed << setprecision(c) << a*1.0/b << endl;
    }
    return 0;
}


@2-10
#include <iostream>
#include <fstream>
#include <string.h>
using namespace std;
ifstream fin("aplusb.in");
ofstream fout("aplusb.out");
int main(void){
    int abc, def, ghi, hash[10];
    for( abc = 123; abc <= 329; abc++){
        memset(hash, 0, sizeof(hash));
        def = 2*abc, ghi = 3*abc;
        hash[def/100] = 1, hash[def%100/10] = 1, hash[def%10] = 1;
        hash[abc/100] = 1, hash[abc%100/10] = 1, hash[abc%10] = 1;
        hash[ghi/100] = 1, hash[ghi%100/10] = 1, hash[ghi%10] = 1;

        int countOne = 0;
        for(int i = 1; i < 10; i++){
            if(hash[i] == 1)
                countOne++;
        }
        if(countOne == 9)
            fout << "abc:def:ghi is:\n" << abc <<":"<< def << ":"<< ghi <<endl;
    }
    return 0;
}