Problem B_Tidy Numbers

[Codejam_2017]Problem B_Tidy Numbers.c

#pragma warning (disable:4996)
#include <stdio.h>
/*
 * 속도 : O(N)
 * 메모리 : O(N)
 */
char num[19];
char ans[19];
int len;
int get_len(char *str) {
	int i = 0;
	while (str[i++]);
	return i-1;
}
void solve() {
	int start_p;
	int end_p = 0;
	int is_same = 0;
	int i;
	int len = get_len(num);
	start_p = len;
	if (len == 1) {
		ans[0] = num[0];
	}
	for (i = 0; i < len-1; ++i) {
		// 상승
		if (num[i] < num[i + 1]) {
			is_same = 0;
			ans[i] = num[i];
		}
		// 같음
		else if (num[i] == num[i + 1]) {
			ans[i] = num[i];
			if (!is_same) {
				is_same = !is_same;
				start_p = i;
			}
		}
		// 하향
		else {
			if (num[i] == '1') {
				start_p = 0;
				end_p = 1;
			}
			else if(is_same){
				ans[start_p] = num[start_p] - 1;
				start_p = start_p + 1;
			}
			else {
				ans[i] = num[i] - 1;
				start_p = i + 1;
			}
			for (i = start_p; i < len - end_p; ++i) {
				ans[i] = '9';
			}
			ans[i] = '\0';
			return;
		}
	}
	ans[len - 1] = num[len - 1];
	ans[len] = '\0';
	return;
}
int main() {
	int testcase;
	scanf("%d", &testcase);
	for (int i = 1; i <= testcase; ++i) {
		scanf("%s", num);
		solve();
		printf("Case #%d: %s\n", i, ans);
	}
	return 0;
}