poj1126

递归

注意：The input consists of a number of sentences consisting only of characters p through z and N, C, D, E, and I.这句话是错的，句子还会包含不合法字符。

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
using namespace std;

#define maxl 500

char st[maxl];

int find(char *st)
{
    if (st[0] <= 'z' && st[0] >= 'p')
        return 1;
    if (st[0] == 'N')
    {
        int x = find(st + 1);
        if (x == -1)
            return x;
        return 1 + x;
    }
    if (st[0] == 'I' || st[0] == 'D' || st[0] == 'E' || st[0] == 'C')
    {
        int x = find(st + 1);
        if (x == -1)
            return x;
        int y = find(st + 1 + x);
        if (y == -1)
            return x;
        return 1 + x + y;
    }
    return -1;
}

int main()
{
    //freopen("t.txt", "r", stdin);
    while (scanf("%s", st) == 1)
    {
        if (find(st) == (signed int)strlen(st))
            printf("YES\n");
        else
            printf("NO\n");
    }
    return 0;
}