1496. Path Crossing.cpp

/*
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'.
*/

class Solution {
public:
    bool isPathCrossing(string path) {
        set<vector<int>> points;
        points.insert({0, 0});
        int a = 0, b = 0;
        for (int i = 0; i < path.size(); i++){
            if (path[i] == 'N')
                b++;
            else if (path[i] == 'E')
                a++;
            else if (path[i] == 'S')
                b--;
            else
                a--;
            if (points.find({a, b}) != points.end())
                return true;
            points.insert({a, b});
        }
        return false;
    }
};