RMQ模板

template<class T>
struct RMQ {
    int n;
    vector<vector<T>> f;
    vector<int> log_2;
    vector<T> a;
    function <T(T, T)> cmp;
    RMQ() {}
    RMQ(int n, function<T(T, T)> op) : 
        n(n), f(n + 5, vector<T>(__lg(n) + 1)), log_2(n + 5), a(n + 5), cmp(op) {}
    RMQ(int n, const vector <T> &_a, function<T(T, T)> op) :
        n(n), f(n + 5, vector<T>(__lg(n) + 1)), log_2(n + 5), a(_a), cmp(op) { init(); }
    void init() {
        int m = __lg(n);
        for(int j = 0; j <= m; j++) {
            for(int i = 1; i + (1 << j) - 1 <= n; i++) {
                if(!j) f[i][j] = a[i];
                else f[i][j] = cmp(f[i][j - 1], f[i + (1 << j - 1)][j - 1]);
            }
        }
        log_2[0] = -1;
        for(int i = 1; i <= n; i++) log_2[i] = log_2[i >> 1] + 1;
    }
    T query(T l, T r) {
        assert(l <= r);
        int k = log_2[r - l + 1];
        return cmp(f[l][k], f[r - (1 << k) + 1][k]);
    }
};