LeetCode Simplify Path

Given an absolute path for a file (Unix-style), simplify it.

For example,
path = "/home/", => "/home"
path = "/a/./b/../../c/", => "/c"

click to show corner cases.

Corner Cases:

• Did you consider the case where path = "/../"?
  In this case, you should return "/".
• Another corner case is the path might contain multiple slashes '/' together, such as "/home//foo/".
  In this case, you should ignore redundant slashes and return "/home/foo".

class Solution {
public:
    string simplifyPath(string path) {
        int len = path.length();
        if (len < 2) return "/";

        vector<string> spath;

        int p = -1, q = 0;

        // seperate the path into parts & simplify it with a stack
        while (q < len) {
            while (q < len && path[q] != '/') q++;
            if (p + 1 < q) {
                add_part_to_spath(path.substr(p + 1, q - p - 1), spath);
            }
            p = q;
            q++;
        }

        // build the final simplified path
        string res;
        for (int i=0; i<spath.size(); i++) {
            res.push_back('/');
            res.append(spath[i]);
        }
        if (res.length() == 0) res = "/";
        return res;

    }

    void add_part_to_spath(string part, vector<string>& spath) {
        if (part == ".") {
            // do nothing;
        } else if (part == "..") {
            // goto the parent path part
            if (!spath.empty()) spath.pop_back();
        } else {
            // enter a new part
            spath.push_back(part);
        }

    }
};

 也可以直接在原有字符串上操作，但还是这样简单明了一些

再写一次：

class Solution {
public:
    string simplifyPath(string path) {
        vector<string> tokens;
        
        int len = path.size();
        
        int last = 0;
        for (int i=0; i<len; i++) {
            char ch = path[i];
            if (ch == '/') {
                if (i - last > 0) {
                    push_token(path.substr(last, i - last), tokens);
                }
                last = i + 1;
            }
        }
        if (len - last > 0) {
            push_token(path.substr(last, len - last), tokens);
        }
        return token_path(tokens);
    }
    
    string token_path(vector<string>& tokens) {
        string path;
        for (string& token : tokens) {
            path = path + "/" + token;
        }
        if (tokens.empty()) {
            path = "/";
        }
        return path;
    }
    
    void push_token(string token, vector<string>& tokens) {
        if (token == ".") {
            // nothing
        } else if (token == "..") {
            if (!tokens.empty()) {
                tokens.pop_back();
            }
        } else {
            tokens.push_back(token);
        }
    }
};