Question

1496. Path Crossing

中文文档

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

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

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;
  }
}

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;
  }
};

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
}

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;
}