CCC 2014 S3

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

int t, n;
int i;

/* Queues */
int mountain[100000], branch[100000];

/* Lengths of queues */
int mountainl, branchl;

/* Last car pushed into the lake */
int lake;

int main(void) {
    /* Read the integer T */
    scanf("%d", &t);

    /* Run code T times */
    while (t--) {
        /* Reset */
        memset(mountain, 0, 100000*sizeof(int));
        memset(branch, 0, 100000*sizeof(int));
        mountainl = branchl = lake = 0;

        /* Read the integer N */
        scanf("%d", &n);
        mountainl = n;

        /* Read the numbers of the next N cars */
        for (i = 0; i < n; i++)
            scanf("%d", &mountain[i]);

        /* Attempt */
        while (1) {
            /* Slide from mountain directly into lake if possible */
            if (mountainl && mountain[mountainl-1] == lake+1) {
                mountain[--mountainl] = 0;
                lake++;
            }

            /* Slide from branch into lake if possible */
            else if (branchl && branch[branchl-1] == lake+1) {
                branch[--branchl] = 0;
                lake++;
            }

            /* Otherwise slide from mountain to branch */
            else if (mountainl) {
                branch[branchl++] = mountain[mountainl-1];
                mountain[--mountainl] = 0;
            }

            else break;
        }

        puts(branchl ? "N" : "Y");
    }
    return 0;
}