UVA 417 - Word Index（数论）

#include <stdio.h>
#include <string.h>
#include <map>
#include <string>
using namespace std;

char str[10];
map<string, int> idx;

void init() {
	memset(str, 0, sizeof(str));
	str[0] = ‘a‘; idx[str] = 1;
	for (int i = 2; i <= 83681; i++) {
		for (int j = 4; j >= 0; j--) {
			if (str[j] != 0) {
				if (str[j] != ‘z‘) str[j]++;
				else {
					int k = j;
					while (k >= 0) {
						if (‘z‘ - str[k] == j - k)
							k--;
						else break;
					}
					if (k != -1) {
						str[k]++;
						for (int l = k + 1; l <= j; l++) {
							str[l] = str[l - 1] + 1;
						}
					}
					else {
						for (int l = 0; l <= j + 1; l++)
							str[l] = ‘a‘ + l;
					}
				}
				idx[str] = i;
				break;
			}
		}
	}
}

int main() {
	init();
	char s[10];
	while (~scanf("%s", s)) {
		if (idx.count(s))
			printf("%d\n", idx[s]);
		else
			printf("0\n");
	}
	return 0;
}