README_EN.md

752. Open the Lock

中文文档

Description

You have a lock in front of you with 4 circular wheels. Each wheel has 10 slots: '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'. The wheels can rotate freely and wrap around: for example we can turn '9' to be '0', or '0' to be '9'. Each move consists of turning one wheel one slot.

The lock initially starts at '0000', a string representing the state of the 4 wheels.

You are given a list of deadends dead ends, meaning if the lock displays any of these codes, the wheels of the lock will stop turning and you will be unable to open it.

Given a target representing the value of the wheels that will unlock the lock, return the minimum total number of turns required to open the lock, or -1 if it is impossible.

 

Example 1:

Input: deadends = ["0201","0101","0102","1212","2002"], target = "0202"
Output: 6
Explanation:
A sequence of valid moves would be "0000" -> "1000" -> "1100" -> "1200" -> "1201" -> "1202" -> "0202".
Note that a sequence like "0000" -> "0001" -> "0002" -> "0102" -> "0202" would be invalid,
because the wheels of the lock become stuck after the display becomes the dead end "0102".

Example 2:

Input: deadends = ["8888"], target = "0009"
Output: 1
Explanation:
We can turn the last wheel in reverse to move from "0000" -> "0009".

Example 3:

Input: deadends = ["8887","8889","8878","8898","8788","8988","7888","9888"], target = "8888"
Output: -1
Explanation:
We can't reach the target without getting stuck.

Example 4:

Input: deadends = ["0000"], target = "8888"
Output: -1

 

Constraints:

• 1 <= deadends.length <= 500
• deadends[i].length == 4
• target.length == 4
• target will not be in the list deadends.
• target and deadends[i] consist of digits only.

Solutions

Python3

class Solution:
    def openLock(self, deadends: List[str], target: str) -> int:
        s = set(deadends)
        if target in s or '0000' in s:
            return -1
        if target == '0000':
            return 0

        def prev(c):
            return '9' if c == '0' else str(int(c) - 1)

        def next(c):
            return '0' if c == '9' else str(int(c) + 1)

        def get(t):
            res = []
            t = list(t)
            for i in range(4):
                c = t[i]
                t[i] = prev(c)
                res.append(''.join(t))
                t[i] = next(c)
                res.append(''.join(t))
                t[i] = c
            return res

        visited = set()
        q = deque([('0000', 0)])
        while q:
            status, step = q.popleft()
            for t in get(status):
                if t in visited or t in s:
                    continue
                if t == target:
                    return step + 1
                q.append((t, step + 1))
                visited.add(t)
        return -1

Java

class Solution {
    public int openLock(String[] deadends, String target) {
        Set<String> s = new HashSet<>(Arrays.asList(deadends));
        if (s.contains(target) || s.contains("0000")) {
            return -1;
        }
        if (Objects.equals(target, "0000")) {
            return 0;
        }
        Set<String> visited = new HashSet<>();
        Deque<String> q = new ArrayDeque<>();
        q.offerLast("0000");
        int step = 0;
        while (!q.isEmpty()) {
            ++step;
            for (int i = 0, n = q.size(); i < n; ++i) {
                String status = q.pollFirst();
                for (String t : get(status)) {
                    if (visited.contains(t) || s.contains(t)) {
                        continue;
                    }
                    if (Objects.equals(t, target)) {
                        return step;
                    }
                    q.offerLast(t);
                    visited.add(t);
                }
            }
        }
        return -1;
    }

    private char prev(char c)  {
        return c == '0' ? '9' : (char) (c - 1);
    }

    private char next(char c) {
        return c == '9' ? '0' : (char) (c + 1);
    }

    private List<String> get(String t) {
        List res = new ArrayList<>();
        char[] chars = t.toCharArray();
        for (int i = 0; i < 4; ++i) {
            char c = chars[i];
            chars[i] = prev(c);
            res.add(String.valueOf(chars));
            chars[i] = next(c);
            res.add(String.valueOf(chars));
            chars[i] = c;
        }
        return res;
    }
}

C++

class Solution {
public:
    int openLock(vector<string>& deadends, string target) {
        unordered_set<string> s(deadends.begin(), deadends.end());
        if (s.count(target) || s.count("0000")) return -1;
        if (target == "0000") return 0;
        unordered_set<string> visited;
        queue<string> q;
        q.push("0000");
        int step = 0;
        while (!q.empty())
        {
            ++step;
            for (int i = 0, n = q.size(); i < n; ++i)
            {
                string status = q.front();
                q.pop();
                for (auto t : get(status))
                {
                    if (visited.count(t) || s.count(t)) continue;
                    if (t == target) return step;
                    q.push(t);
                    visited.insert(t);
                }
            }
        }
        return -1;
    }

    char prev(char c) {
        return c == '0' ? '9' : (char) (c - 1);
    }

    char next(char c) {
        return c == '9' ? '0' : (char) (c + 1);
    }

    vector<string> get(string& t) {
        vector<string> res;
        for (int i = 0; i < 4; ++i)
        {
            char c = t[i];
            t[i] = prev(c);
            res.push_back(t);
            t[i] = next(c);
            res.push_back(t);
            t[i] = c;
        }
        return res;
    }
};

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