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1496. Path Crossing

Description

Given a string path, where path[i] = 'N', 'S', 'E' or 'W', each representing moving one unit north, south, east, or west, respectively. You start at the origin (0, 0) on a 2D plane and walk on the path specified by path.

Return true if the path crosses itself at any point, that is, if at any time you are on a location you have previously visited. Return false otherwise.

 

Example 1:

Input: path = "NES"
Output: false 
Explanation: Notice that the path doesn't cross any point more than once.

Example 2:

Input: path = "NESWW"
Output: true
Explanation: Notice that the path visits the origin twice.

 

Constraints:

  • 1 <= path.length <= 104
  • path[i] is either 'N', 'S', 'E', or 'W'.

Solutions

Solution 1

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class Solution:
    def isPathCrossing(self, path: str) -> bool:
        i = j = 0
        vis = {(0, 0)}
        for c in path:
            match c:
                case 'N':
                    i -= 1
                case 'S':
                    i += 1
                case 'E':
                    j += 1
                case 'W':
                    j -= 1
            if (i, j) in vis:
                return True
            vis.add((i, j))
        return False

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class Solution {
    public boolean isPathCrossing(String path) {
        int i = 0, j = 0;
        Set<Integer> vis = new HashSet<>();
        vis.add(0);
        for (int k = 0, n = path.length(); k < n; ++k) {
            switch (path.charAt(k)) {
                case 'N' -> --i;
                case 'S' -> ++i;
                case 'E' -> ++j;
                case 'W' -> --j;
            }
            int t = i * 20000 + j;
            if (!vis.add(t)) {
                return true;
            }
        }
        return false;
    }
}

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class Solution {
public:
    bool isPathCrossing(string path) {
        int i = 0, j = 0;
        unordered_set<int> s{{0}};
        for (char& c : path) {
            if (c == 'N') {
                --i;
            } else if (c == 'S') {
                ++i;
            } else if (c == 'E') {
                ++j;
            } else {
                --j;
            }
            int t = i * 20000 + j;
            if (s.count(t)) {
                return true;
            }
            s.insert(t);
        }
        return false;
    }
};

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func isPathCrossing(path string) bool {
    i, j := 0, 0
    vis := map[int]bool{0: true}
    for _, c := range path {
        switch c {
        case 'N':
            i--
        case 'S':
            i++
        case 'E':
            j++
        case 'W':
            j--
        }
        if vis[i*20000+j] {
            return true
        }
        vis[i*20000+j] = true
    }
    return false
}

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function isPathCrossing(path: string): boolean {
    let [i, j] = [0, 0];
    const vis: Set<number> = new Set();
    vis.add(0);
    for (const c of path) {
        if (c === 'N') {
            --i;
        } else if (c === 'S') {
            ++i;
        } else if (c === 'E') {
            ++j;
        } else if (c === 'W') {
            --j;
        }
        const t = i * 20000 + j;
        if (vis.has(t)) {
            return true;
        }
        vis.add(t);
    }
    return false;
}

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