单调栈和单调队列

class Solution {
public:
    /**
     * @param arr: the arr
     * @return: the sum of the luck number
     */
    static bool pairComByFirst(pair<int, int>a, pair<int, int>b) {
        return a.first < b.first;
    }
    int luckNumber(vector<int>& arr) {
        int n = arr.size();
        int ans = 0;
        vector<pair<int, int>> a;
        for (int i = 0; i < n; i++) {
            a.emplace_back(pair<int, int>(arr[i], i));
        }
        sort(a.begin(), a.end(), pairComByFirst);
        vector<int> l(n, 0), r(n, 0);
        stack<pair<int, int>> s;
        pair<int, int> fir(0, 0);
        for (int i = 0; i < n; i++) {
            while (!s.empty()) {
                fir = s.top();
                if (a[i].second < fir.second) {
                    l[fir.second] = a[i].first;
                    s.pop();
                }
                else {
                    break;
                }
            }
            s.push(a[i]);
        }
        while (!s.empty()) {
            s.pop();
        }
        for (int i = n - 1; i >= 0; i--) {
            while (!s.empty()) {
                fir = s.top();
                if (a[i].second > fir.second) {
                    r[fir.second] = a[i].first;
                    s.pop();
                }
                else {
                    break;
                }
            }
            s.push(a[i]);
        }
        for (int i = 1; i < n - 1; i++) {
            if (l[i] && r[i] && l[i] % r[i] == 0) {
                ans++;
            }
        }
        return ans;
    }
};