ACM 10763 - Foreign Exchange

#include <stdio.h>
#include <memory.h>

int data[300] = {0};

int main()
{
    int n, i, j, ConfirmCount, NotConfirmCount;
    while (scanf("%d", &n) == 1)
    {
        if (n == 0) break;
        memset(data, 0, 300);
        ConfirmCount = 0, NotConfirmCount = 0;
        while (n --)
        {
            scanf("%d %d", &i, &j);
            if (data[i] >= 0)
               data[i] ++, ConfirmCount ++;
            else data[i] ++, NotConfirmCount --;
            if (data[j] <= 0)
               data[j] --, NotConfirmCount ++;
            else data[j] --, ConfirmCount --;      
        }
        
        if (ConfirmCount == 0 && NotConfirmCount == 0)
           printf("YES\n");
        else printf("NO\n");   
    }
    return 0;
}

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