EPOCH Qualifier

Problem1.c

#include <stdio.h>
#include <stdlib.h>

int compare(const void *a, const void *b)
{
	return (*(int *)b - *(int *)a);
}

int main(void)
{
	int i = 0, j = -1, k = 0, n;
	int *a, *b;
	scanf("%d", &n);
	a = malloc(sizeof(int) * n);
	b = malloc(sizeof(int) * n);
	for(i = 0; i < n; i++)
		scanf("%d", &a[i]);
	qsort(a, n, sizeof(int), compare);
	for(i = 0; i < n; i++) {
		if(j == -1)
			if(a[i] == a[i + 1])
				j = a[i];
			else
				b[k++] = a[i];
		else
			if(j - 1 < k)
				break;
			else if(a[i] != a[i + 1])
				b[k++] = a[i];
		while(a[i] == a[i + 1])
			i++;
	}
	if(j != -1 && j - 1 < k)
		printf("%d\n", b[j - 1]);
	else
		printf("%d\n", b[k - 1]);
	return 0;
}

Problem2.c

#include <stdio.h>
#include <string.h>

int main(void)
{
	int i, j, k, l, m, n;
	long long int point = 0;
	char a[256], b[256];
	scanf("%d%s", &n, b);
	for(i = 0; i < n - 1; i++) {
		strcpy(a, b);
		scanf("%s", b);
		j = strlen(a);
		k = strlen(b);
		l = 0;
		if(j == k) {
			for(m = 0; m < j; m++) {
				if(a[m] != b[m]) {
					l++;
					if(l > 1)
						break;
				}
			}
			if(l == 0)
				point *= 2;
			else if(l == 1)
				point += 2;
			else
				point = 0;
		} else if(j == k - 1) {
			for(m = 0; m < k; m++) {
				if(a[l] == b[m])
					l++;
				if(m - l > 1)
					break;
			}
			if(m - l == 1)
				point++;
			else
				point = 0;
		} else if(j == k + 1) {
			for(m = 0; m < j; m++) {
				if(a[m] == b[l])
					l++;
				if(m - l > 1)
					break;
			}
			if(m - l == 1)
				point--;
			else
				point = 0;
		} else {
			point = 0;
		}
	}
	printf("%lld\n", point);
	return 0;
}

Problem3.c

#include<stdio.h>
#include<string.h>

int checksum(const char *nums, int plus, int equal, int last)
{
	int a = 1, b = 1, c = 1, d = 0, i = 0, x, y, z;
	while(a || b || c) {
		if(!a || i >= plus) {
			a = 0;
			x = 0;
		} else {
			x = *(nums + plus - i - 1) - '0';
		}
		if(!b || i >= equal - plus) {
			b = 0;
			y = 0;
		} else {
			y = *(nums + equal - i - 1) - '0';
		}
		if(!c || i >= last - equal) {
			c = 0;
			z = 0;
		} else {
			z = *(nums + last - i - 1) - '0';
		}
		if((d + x + y) % 10 == z) {
			d = (d + x + y) / 10;
			i++;
		} else {
			return 0;
		}
	}
	return 1;
}

int main(void)
{
	char num[1000];
	int comp, equal, firstpos, last, n, plus, pluspos, res = 0;
	scanf("%d", &n);
	while(n--) {
		scanf("%s", num);
		last = strlen(num);
		firstpos=0;
		while(num[firstpos] == '0')
			firstpos++;
		comp = 1;
		for(plus = 1; plus - firstpos <= (last - firstpos) / 2 && comp; plus++) {
			if(plus - firstpos > (last - plus) / 2) {
				equal = last - (plus - firstpos);
			} else {
				pluspos = plus;
				while(num[pluspos] == '0')
					pluspos++;
				if(plus - firstpos > (last - pluspos) / 2)
					equal = last - (plus -firstpos);
				else
					equal = pluspos + (last - pluspos) / 2;
			}
			do{
				if(checksum(num, plus, equal, last) || checksum(num, plus, equal-1, last)) {
					comp = 0;
					res++;
					break;
				}
				equal -= 2;
			} while(num[equal] == '0');
		}
	}
	printf("%d\n", res);
	return 0;
}