USACO运行时错误：非法文件打开（/ dev / tty）

Question

我在USACO上解决了一个问题，分级员给了我以下错误：

  

运行1：执行错误：您的程序出现此运行时错误：           非法文件打开（/ dev / tty）。该程序运行0.003 CPU           错误前几秒。它使用了2164 KB的内存。

根据USACO帮助页面，错误与越界数组索引有关。我用几个测试用例成功测试了我的代码，并且我一直小心边界和数组索引，但不幸的是我找不到错误。有什么建议吗？

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

int main(){
    int i, flag, flag2, lcount, rcount, gcount, nbeads, start;
    char right, left, necklace[800];

    FILE *fin  = fopen ("beads.in", "r");
    FILE *fout = fopen ("beads.out", "w");

    fscanf(fin, "%d %s", &nbeads, necklace);
    strcat(necklace,necklace);
    necklace[2*nbeads] = '\0';

    flag = 1;
    left = right = ' ';
    start = gcount = 0;

    // First cut
    for(i = start, lcount = 0; necklace[i] != right && i < nbeads; i++, lcount++)
        if((flag) && (necklace[i] != 'w')){
            left = necklace[i];
            right = (left == 'b') ? 'r' : 'b';
            flag--;
        }           

    gcount = lcount;
    if(i < nbeads){
        // Remaining cuts
        flag = 2;
        flag2 = 0;

        for(start = i; start > 0 && necklace[start - 1] == 'w'; start--, lcount--);
        while(flag){                            
            for(i = start, rcount = 0; necklace[i] != left && i < 2*nbeads; i++, rcount++);
            gcount = (gcount < lcount + rcount) ? lcount + rcount : gcount;
            lcount = rcount;
            right = (right == 'b') ? 'r' : 'b';
            left = (left == 'b') ? 'r' : 'b';
            for(start = i; start > 0 && necklace[start - 1] == 'w'; start--, lcount--);                     
            if(!flag2 && start >= nbeads){
                gcount -= (i - nbeads);
                break;
            }
            flag2++;
            if(start >= nbeads) flag--;         
        }
    }

    fprintf(fout, "%d", gcount);

    fclose(fin);
    fclose(fout);

    return 0;   
}