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by Sumit Chourasia | Oct 02, 2020 | Category :coding | Tags : algorithm data-structure easy leetcode string

Path Crossing - String - Easy - LeetCode

Path Crossing - String - Easy - LeetCode

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}

public class Solution {
    public bool IsPathCrossing(string path) {
        int x = 0;
        int y = 0;
        var set = new HashSet<string>();
        set.Add(GetKey(x,y));
        for(int i=0;i<path.Length;i++){
            switch(path[i]){
                case 'E':
                    x++;
                    break;
                case 'W':
                    x--;
                    break;
                case 'N':
                    y++;
                    break;
                case 'S':
                    y--;
                    break;
            }
            if(set.Contains(GetKey(x,y))){
                return true;
            }
            set.Add(GetKey(x,y));
        }
        
        return false;
    }
    
    private string GetKey(int x, int y){
        return x.ToString()+":"+y.ToString();
    }
}

Time Complexity: O(n)

Space Complexity: O(n)

 

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