Luogu P1465 序言页码（罗马数字打表）

楼下的打表不太好理解，来一发好写又好理解的打表方法。

罗马数字的构造方法：

每一位之间没有关系，可以分别处理，直接把千位、百位、十位、个位按顺序放就可以。0直接跳过
例如：123：CXXIII
每一位上的数字的表示方法：
“表示方法”列中以个位为例，1=I，5=V，10=X，n表示这一位上的数字，十位百位以此类推。

打表关键代码

s[i][j]表示右数第i位（个位i=1）上的j的表示方法，注意数组赋初值的格式。

string s[5][11]={ //注意每一位上的0都给出空字符串，方便操作
    {},    //空出第0行
    {"","I","II","III","IV","V","VI","VII","VIII","IX"}, //个位
    {"","X","XX","XXX","XL","L","LX","LXX","LXXX","XC"}, //十位
    {"","C","CC","CCC","CD","D","DC","DCC","DCCC","CM"}, //百位
    {"","M","MM","MMM"}  //千位（打3个就可以满足题目要求）
};

对每一个数进行计数：（uint是unsigned int）

void Calc(int n){
    int now=1; //当前的数位
    while(n>0){
        Count(s[now][n%10]); //将字符串计数
        now++,n/=10;         //下一位
    }
}

完整代码：

#include <cstdio>
#include <string>
#include <iostream>
typedef unsigned int uint;
using namespace std;
string s[5][11]={
    {},
    {"","I","II","III","IV","V","VI","VII","VIII","IX"},
    {"","X","XX","XXX","XL","L","LX","LXX","LXXX","XC"},
    {"","C","CC","CCC","CD","D","DC","DCC","DCCC","CM"},
    {"","M","MM","MMM"}
};
string ap="IVXLCDM";  //罗马数字列表，方便输出
int c[300];           //统计数组
void Count(string s){ //将字符串每一位统计
    for(uint i=0;i<s.size();i++) c[(uint)s[i]]++;
}
void Calc(int n){
    int now=1;
    while(n>0){
        Count(s[now][n%10]);
        now++,n/=10;
    }
}
int main(){
    int n;
    scanf("%d",&n);
    for(int i=1;i<=n;i++) Calc(i); //对每一个数字统计
    for(uint i=0;i<ap.size();i++){ //按顺序输出
        if(c[(uint)ap[i]]>0) //有这个字母
            printf("%c %d\n",ap[i],c[(uint)ap[i]]);
    }
    return 0;
}

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