1496. Path Crossing

1496. Path Crossing (Easy)

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've 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 <= 10^4
• path will only consist of characters in {'N', 'S', 'E', 'W}

Related Topics:
String

Solution 1.

// OJ: https://leetcode.com/problems/path-crossing/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(N)
class Solution {
    long hash(int x, int y) { return (long)x * 10000 + y; }
public:
    bool isPathCrossing(string path) {
        unordered_set<long> s;
        int x = 0, y = 0;
        s.insert(hash(x, y));
        for (char c : path) {
            if (c == 'N') ++y;
            else if (c == 'E') ++x;
            else if (c == 'S') --y;
            else --x;
            long key = hash(x, y);
            if (s.count(key)) return true;
            s.insert(key);
        }
        return false;
    }
};