1496. Path Crossing

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.

class Solution {
public:
    bool isPathCrossing(string path) {
        set<pair<int,int>> st;
        int x = 0, y = 0;
        auto move = [&](char p) {
            if(p == 'N') y += 1;
            else if(p == 'S') y -= 1;
            else if(p == 'E') x += 1;
            else if(p == 'W') x -= 1;
        };
        auto ok = [&]() {
            if(st.count({x,y})) return true;
            st.insert({x,y});
            return false;
        };
        ok();
        for(auto& p : path) {
            move(p);
            if(ok()) return true;
        }
        return false;
    }
};