我怎样才能让这个网格环绕四周？

Question

我有一个作业需要让用户创建网格的高度和宽度。 然后能够在任何 x 和 y 坐标处将“船”放置到该网格上。 然后你可以在该网格的某个部分放置风暴，然后提示并查看风暴是否与船只重叠。 我已经成功地做到了，但我无法让风暴环绕网格。 例如，如果网格是 20x20 并且我在第 20 个位置开始的风暴应该转移到网格左侧的 1 position。 这是代码，我有它的外观图。 （注意没有物理网格被打印到终端）

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

typedef struct ship {
    // Declaring variables
    char shipName[21]; 
    int x, y, w, h;  
    char direction;      
    struct ship *next;
} Ship;

//Declaring head of linked list
Ship *head = NULL;

void newShip(int x, int y, char direction, char *shipName) {
    //Adding ships to linked list
    Ship *new_ship = (Ship *)malloc(sizeof(Ship));
    strcpy(new_ship->shipName, shipName);
    new_ship->x = x;
    new_ship->y = y;
    new_ship->direction = direction;
    new_ship->next = head;
    head = new_ship;
}

void shipMovement(int time, int w, int h) {
    //Moving ships
    Ship *current = head;
    while (current != NULL) {
        if (current->direction = 'U') {
            current->y = (current->y + time) % h;
        }
        else if (current->direction = 'D') {
            current->y = (current->y - time + h) % h;
        }
        else if (current->direction = 'L') {
            current->x = (current->x - time + w) % w;
        }
        else if (current->direction = 'R') {
            current->x = (current->x + time) % w;
        }
        else {
            printf("Invalid Direction!\n");
        }
        current = current->next;
    }
}

void checkAffShips(int x, int y, int w, int h, char **affShips, int *numAffShips) {
    //Checking if ships are affected by storm
    Ship *current = head;
    while (current != NULL) {
        if (((current->x >= x) && (current->x < x + w)) && ((current->y >= y) && (current->y < y + h))) {
            // add shipName to list of affected ships
            affShips[*numAffShips] = (char *)malloc(sizeof(char) * 21);
            strcpy(affShips[(*numAffShips)++], current->shipName);
        }
        current = current->next;
    }
}

//Main Function------------------------------------------------------------------
int main() {
    int w, h;
    int stormWidth, stormHeight;
    scanf("%d %d", &w, &h);
    char userInput;
    //Looping through commands
    while (scanf(" %c", &userInput) != 4) {
        if (userInput == '1') {
            int x, y;
            char direction[21], shipName[21];
            scanf("%d %d %s %s", &x, &y, direction, shipName);
            newShip(x, y, direction[0], shipName);
        } else if (userInput == '2') {
            int time;
            scanf("%d", &time);
            shipMovement(time, w, h);
        } else if (userInput == '3') {
            int x, y, w, h;
            scanf("%d %d %d %d", &x, &y, &w, &h);
            char *affShips[1000];
            int numAffShips = 0;
            checkAffShips(x, y, w, h, affShips, &numAffShips);
            printf("%d\n", numAffShips);
            for (int i = 0; i < numAffShips; i++) {
                printf("%s\n", affShips[i]);
                free(affShips[i]);
            }
        } else if (userInput == '4') {
            break;
        }
        else {
            printf("Invalid Input!\n");
        }
    }
    return 0;
}

这是文档：（ https://i.stack.imgur.com/K28We.png ）

我已经尝试了很多不同的东西，所以也许我只是在我的尝试中没有做正确的事情，但我相信有人可以帮助解决这个问题。

Answer 1

您对受影响船只的测试是错误的。 在您的示例中，如果右下角(19, 19)有大小为 2 的风暴，则不会捕获左上角(0, 0)的船，因为0不在[19, 21) 。

解决此问题的一种方法是将要测试的点移动到“扩展范围”（如果它位于风暴起点下方）。 （“扩展范围”是不换行的范围，因此扩展到板宽度的两倍。）

因此，要测试一维点是否位于循环范围内，您可以像这样使用 function：

int in_cyclic_range(int n, int lower, int width, int wrap)
{
    if (n < lower) n += wrap;

    return (n < lower + width);
}

如果您现在使用in_cyclic_range(n, 19, 2, 20) 19宽度为2的风暴上从[0, 20)的整个范围内测试n ，您将在位置19和0处获得命中。

Answer 2

为了测试一艘船是否受到风暴的影响，您需要风暴 position 和维度，船舶 position和网格维度。

在您的代码中，您使用w和h作为网格维度，并在if (userInput == '3') {... }的本地 scope 中使用一组新变量w和h作为风暴维度。 这很令人困惑，并使这部分代码无法访问网格维度。 您应该为风暴维度使用stormWidth和stormHeight ，并将这些维度和网格维度传递给checkAffShips function。

checkAffShips中包裹坐标系的测试比您为考虑风暴区域的包裹部分而编写的测试更复杂：多达 3 个额外的矩形。

还要注意这些问题：

• 为网格和风暴维度使用明确的名称将有助于避免混淆。
• Ship结构中的w和h字段未使用。
• 应该通过在 null 终止符之前指定要存储到目标数组中的最大字符数来保护使用scanf读取字符串。
• newShip不应直接使用strcpy ，因为shipName参数可能比目标数组长。
• 您应该检查scanf()的返回值以检测无效或丢失的输入。
• if (current->direction = 'U')设置current->direction并评估为 true。 你应该使用==而不是=
• 船名数组affShips应由checkAffShips分配。

这是修改后的版本：

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

typedef struct ship {
    char shipName[21];
    int x, y;
    char direction;
    struct ship *next;
} Ship;

//Declaring head of linked list
Ship *head = NULL;

/* string copy function with size limitation */
void mystrcpy(char *dest, size_t size, const char *src) {
    while (size > 1) {
        *dest++ = *src++;
        size--;
    }
    if (size > 0)
        *dest = '\0';
}

void newShip(int x, int y, char direction, const char *shipName) {
    //Adding ship to linked list
    Ship *new_ship = (Ship *)malloc(sizeof(*new_ship));
    if (new_ship) {
        mystrcpy(new_ship->shipName, sizeof new_ship->shipName, shipName);
        new_ship->x = x;
        new_ship->y = y;
        new_ship->direction = direction;
        new_ship->next = head;
        head = new_ship;
    }
}

void shipMovement(int time, int w, int h) {
    //Moving ships
    for (Ship *current = head; current != NULL; current = current->next) {
        if (current->direction == 'U') {
            current->y = (current->y + time) % h;
        } else
        if (current->direction == 'D') {
            current->y = (current->y + h - time % h) % h;
        } else
        if (current->direction == 'L') {
            current->x = (current->x + w - time % w) % w;
        } else
        if (current->direction == 'R') {
            current->x = (current->x + time) % w;
        } else {
            printf("%s: invalid Direction '%c'!\n",
                   current->shipName, current->direction);
        }
    }
}

char **checkAffShips(int stormX, int stormY, int stormWidth, int stormHeight,
                     int gridWidth, int gridHeight,
                     int *pnumAffShips)
{
    char **affShips = NULL;
    int numAffShips = 0;
    for (Ship *current = head; current != NULL; current = current->next) {
        int x = current->x;
        int y = current->y;
        //Checking if ship is affected by storm
        if (((x >= stormX && x < stormX + stormWidth) ||
             (stormX + stormWidth > gridWidth && x < (stormX + stormWidth) % gridWidth)) &&
            ((y >= stormY && y < stormY + stormHeight) ||
             (stormY + stormHeight > gridHeight && y < (stormY + stormHeight) % gridHeight)))
        {
            // add shipName to list of affected ships
            affShips = realloc(affShips, sizeof(*affShips) * (numAffShips + 1));
            affShips[numAffShips++] = strdup(current->shipName);
        }
    }
    *pnumAffShips = numAffShips;
    return affShips;
}

//Main Function------------------------------------------------------------------
int main() {
    int gridWidth, gridHeight;
    if (scanf("%d %d", &gridWidth, &gridHeight) != 2)
        return 1;
    char userInput;
    //Looping through commands
    while (scanf(" %c", &userInput) == 1) {
        if (userInput == '1') {
            int x, y;
            char direction[21], shipName[21];
            if (scanf("%d %d %20s %20s", &x, &y, direction, shipName) != 4)
                return 1;
            newShip(x, y, direction[0], shipName);
        } else
        if (userInput == '2') {
            int time;
            if (scanf("%d", &time) != 1)
                return 1;
            shipMovement(time, gridWidth, gridHeight);
        } else
        if (userInput == '3') {
            int x, y, stormWidth, stormHeight;
            if (scanf("%d %d %d %d", &x, &y, &stormWidth, &stormHeight) != 4)
                return 1;
            char **affShips;
            int numAffShips = 0;
            affShips = checkAffShips(x, y, stormWidth, stormHeight,
                                     gridWidth, gridHeight, &numAffShips);
            printf("%d\n", numAffShips);
            for (int i = 0; i < numAffShips; i++) {
                printf("%s\n", affShips[i]);
                free(affShips[i]);
            }
            free(affShips);
        } else
        if (userInput == '4') {
            break;
        } else {
            printf("Invalid Input!\n");
        }
    }
    return 0;
}