838

class Solution {
public:
    string pushDominoes(string A) {
        int n = A.size();
        int dist[n];
        memset(dist, 0, sizeof(dist));

        // dist from left.
        int force = 0;
        for(int i=0; i<n; i++){
            if(A[i] == 'R') force = n;
            else if(A[i] == 'L') force = 0;
            else force = max(force-1, 0);
            dist[i] += force;
        }

        // dist from right.
        force = 0;
        for(int i=n-1; i>=0; i--){
            if(A[i] == 'L') force = n;
            else if(A[i] == 'R') force = 0;
            else force = max(force-1, 0);
            dist[i] -= force;
        }

        string ans = "";
        for(int i=0; i<n; i++){
            if(dist[i] > 0) ans += "R";
            else if(dist[i] < 0) ans += "L";
            else ans += ".";
        }
        return ans;
    }
};