71. Simplify Path

Problem

Tags: String, Stack

Given a string path, which is an absolute path (starting with a slash '/') to a file or directory in a Unix-style file system, convert it to the simplified canonical path.

In a Unix-style file system, a period '.' refers to the current directory, a double period '..' refers to the directory up a level, and any multiple consecutive slashes (i.e. '//') are treated as a single slash '/'. For this problem, any other format of periods such as '...' are treated as file/directory names.

The canonical path should have the following format:

• The path starts with a single slash '/'.
• Any two directories are separated by a single slash '/'.
• The path does not end with a trailing '/'.
• The path only contains the directories on the path from the root directory to the target file or directory (i.e., no period '.' or double period '..')

Return the simplified canonical path.

Example 1:

Input: path = "/home/"
Output: "/home"
Explanation: Note that there is no trailing slash after the last directory name.

Example 2:

Input: path = "/../"
Output: "/"
Explanation: Going one level up from the root directory is a no-op, as the root level is the highest level you can go.

Example 3:

Input: path = "/home//foo/"
Output: "/home/foo"
Explanation: In the canonical path, multiple consecutive slashes are replaced by a single one.

Constraints:

• 1 <= path.length <= 3000
• path consists of English letters, digits, period '.', slash '/' or '_'.
• path is a valid absolute Unix path.

Solution

Solution

I use stack to store the path slices, but I think deque will be a better choice because we need to construct the output canonical path in the same order with the given absolute one.

The rules are simple:

1. "..": pop last one.
2. "." and "": do nothing.
3. otherwise, push it.

Then we construct the canonical path by directly access the stack data (not a good way, but works because the underlying structure of my stack).

Code

C

// 71. Simplify Path (10/5/54168)
// Runtime: 0 ms (94.52%) Memory: 6.97 MB (20.55%) 

#define StructStack(_name, _type) \
    typedef struct _name { \
        _type* data; \
        uint64_t size; \
        uint64_t max; \
        void (*push)(struct _name*, _type); \
        _type (*pop)(struct _name*); \
        _type (*top)(struct _name*); \
        uint8_t (*empty)(struct _name*); \
        void (*clear)(struct _name*); \
        void (*free)(struct _name*); \
    } _name; \
    void push_##_name(_name* stack, _type val) { \
        if (stack->size == stack->max) { \
            return; \
        } \
        stack->data[stack->size++] = val; \
    } \
    _type pop_##_name(_name* stack) { \
        if (stack->size == 0) { \
            return 0; \
        } \
        return stack->data[--stack->size]; \
    } \
    _type top_##_name(_name* stack) { \
        if (stack->size == 0) { \
            return 0; \
        } \
        return stack->data[stack->size - 1]; \
    } \
    uint8_t empty_##_name(_name* stack) { \
        return stack->size == 0; \
    } \
    void clear_##_name(_name* stack) { \
        stack->size = 0; \
    } \
    void free_##_name(_name* stack) { \
        free(stack->data); \
        free(stack); \
    } \
    _name* create_##_name(uint64_t max_size) { \
        _name* stack = malloc(sizeof(_name)); \
        stack->data = calloc(max_size, sizeof(_type)); \
        stack->size = 0; \
        stack->max = max_size; \
        stack->push = &push_##_name; \
        stack->pop = &pop_##_name; \
        stack->top = &top_##_name; \
        stack->empty = &empty_##_name; \
        stack->clear = &clear_##_name; \
        stack->free = &free_##_name; \
        return stack; \
    }

StructStack(Stack, char*);

char* simplifyPath(char* path) {
    char* absolute = malloc(strlen(path) + 1);
    strcpy(absolute, path);

    Stack* stk = create_Stack(strlen(path) / 2);

    char* token = strtok(absolute, "/");
    while (token) {
        if (strcmp(token, "..") == 0) {
            stk->pop(stk);
        }
        else if (strlen(token) && strcmp(token, ".") != 0) {
            stk->push(stk, token);
        }
        token = strtok(NULL, "/");
    }

    char* canonical = calloc(strlen(path) + 1, sizeof(char));
    for (int i = 0; i < stk->size; i++) {
        strcat(canonical, "/");
        strcat(canonical, stk->data[i]);
    }

    if (strlen(canonical) == 0) {
        strcat(canonical, "/");
    }

    free(absolute);
    stk->free(stk);

    return canonical;
}