基本情報技術者試験 C言語問題のソースコード（平成３０年 秋期 ）

#include <stddef.h>

/* 動作確認用に追加 */
#include <stdlib.h>
#include <stdio.h>

#define RED (0)
#define GREEN (1)

struct block_info {
    struct train_info *train;
    struct block_info *next[2];
    int signal;
};

struct train_info {
    int number;
    struct block_info* dest;
};

void set_signals(struct block_info[], int);
void proceed(struct block_info[], int);
int find_block(struct block_info*, struct block_info*);
void start(struct block_info[], int);
void printBlocks(struct block_info[], int);

void set_signals(struct block_info blocks[], int nblocks) {
    int i;
    struct block_info* block;
    for (i = 0; i < nblocks; i++) {
        block = &blocks[i];
        if (block->train == NULL) {  /* 設問1の(a) */
            block->signal = GREEN;
        }
        else {
            block->signal = RED;
        }
    }
}

void proceed(struct block_info blocks[], int nblocks) {
    int i, j;
    struct block_info* block;
    for (i = nblocks - 1; i >= 0; i--) {
        block = &blocks[i];
        if (block->train == NULL) {
            continue;
        }
        if (block == block->train->dest) {
            block->train = NULL;
            continue;
        }
        for (j = 0; j < 2; j++) {
            if (block->next[j] == NULL) {
                continue;
            }
            if (block->next[j]->signal == RED) {
                continue;
            }
            if (find_block(block->next[j], block->train->dest) == 1) {
                block->next[j]->train = block->train;
                block->next[j]->signal = RED;
                block->train = NULL;
                break; /* 設問２の(c) */
            }
        }
    }
}

int find_block(struct block_info* block, struct block_info* dest) {
    int i ;
    if (block == dest) {
        return 1;
    }
    for (i = 0; i < 2; i++) {
        if (block->next[i] == NULL) {
            continue;
        }
        if (find_block(block->next[i], dest) == 1) {
            return 1;
        }
    }
    return 0;
}

void start(struct block_info blocks[], int nblocks) {
    int i;
    set_signals(blocks, nblocks);
    for (i = 0; i < 4; i++) {
        proceed(blocks, nblocks);

        /* 動作確認用に追加 */
        printf("i = %dの時のproceed()実行後の各区間の状態\n", i);
        printBlocks(blocks, nblocks);

        set_signals(blocks, nblocks);

        /* 動作確認用に追加 */
        printf("i = %dの時のset_signals()実行後の各区間の状態\n", i);
        printBlocks(blocks, nblocks);
    }
}

/* 動作確認用に追加 */
void printBlocks(struct block_info blocks[], int nblocks) {
  int i;
  for (i = 0; i < nblocks; i++) {
    printf("　・区間[%d]の情報\n", i);
    if (blocks[i].train != NULL) {
        printf("　　列車[%d]が停車\n", blocks[i].train->number);
    }
    if (blocks[i].signal == RED) {
      printf("　　信号の色は[赤]\n");
    }
    else {
      printf("　　信号の色は[緑]\n");
    }
  }
}

/* 動作確認用に追加 */
int main(void) {
    struct block_info blocks[9];
    struct train_info train[5];

    /* 表１記載の区間情報をblocks[]に格納 */
    blocks[0].train = &train[4];
    blocks[0].train->dest = &blocks[8];
    blocks[0].train->number = 4;
    blocks[0].next[0] = &blocks[2];
    blocks[0].next[1] = NULL;
    blocks[0].signal = RED;

    blocks[1].train = &train[3];
    blocks[1].train->dest = &blocks[5];
    blocks[1].train->number = 3;
    blocks[1].next[0] = &blocks[2];
    blocks[1].next[1] = NULL;
    blocks[1].signal = RED;

    blocks[2].train = NULL;
    blocks[2].next[0] = &blocks[3];
    blocks[2].next[1] = NULL;
    blocks[2].signal = GREEN;

    blocks[3].train = &train[2];
    blocks[3].train->dest = &blocks[6];
    blocks[3].train->number = 2;
    blocks[3].next[0] = &blocks[4];
    blocks[3].next[1] = &blocks[7];
    blocks[3].signal = RED;

    blocks[4].train = &train[1];
    blocks[4].train->dest = &blocks[5];
    blocks[4].train->number = 1;
    blocks[4].next[0] = &blocks[5];
    blocks[4].next[1] = &blocks[6];
    blocks[4].signal = RED;

    blocks[5].train = NULL;
    blocks[5].next[0] = NULL;
    blocks[5].next[1] = NULL;
    blocks[5].signal = GREEN;

    blocks[6].train = NULL;
    blocks[6].next[0] = NULL;
    blocks[6].next[1] = NULL;
    blocks[6].signal = GREEN;

    blocks[7].train = NULL;
    blocks[7].next[0] = &blocks[8];
    blocks[7].next[1] = NULL;
    blocks[7].signal = GREEN;

    blocks[8].train = &train[0];
    blocks[8].train->dest = &blocks[8];
    blocks[8].train->number = 0;
    blocks[8].next[0] = NULL;
    blocks[8].next[1] = NULL;
    blocks[8].signal = RED;

    start(blocks, 9);

    return 0;
}