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)
