3694. Distinct Points Reachable After Substring Removal

You are given a string s consisting of characters 'U', 'D', 'L', and 'R', representing moves on an infinite 2D Cartesian grid.

• 'U': Move from (x, y) to (x, y + 1).
• 'D': Move from (x, y) to (x, y - 1).
• 'L': Move from (x, y) to (x - 1, y).
• 'R': Move from (x, y) to (x + 1, y).

You are also given a positive integer k.

You must choose and remove exactly one contiguous substring of length k from s. Then, start from coordinate (0, 0) and perform the remaining moves in order.

Return an integer denoting the number of distinct final coordinates reachable.

class Solution {
public:
    int distinctPoints(string s, int k) {
        unordered_set<long long> mask;
        long long y = 0, x = 0;
        auto update = [&](int pos, int op) {
            if(s[pos] == 'U') y += op;
            if(s[pos] == 'D') y -= op;
            if(s[pos] == 'R') x += op;
            if(s[pos] == 'L') x -= op;
        };
        
        for(int i = 0; i < s.length(); i++) {
            update(i,1);
            if(i >= k) update(i-k,-1);
            if(i + 1 >= k) {
                long long bit = (abs(y)<<17) + abs(x);
                if(y < 0) bit ^= 1ll<<37;
                if(x < 0) bit ^= 1ll<<36;
                mask.insert(bit);
            }
            
        }
        return mask.size();
    }
};