Problem:
RSQ and RUQ

Write a program which manipulates a sequence $A$ = {$a_0, a_1, ..., a_{n-1}$} with the following operations:

$update(s, t, x)$: change $a_s, a_{s+1}, ..., a_t$ to $x$.

$getSum(s, t)$: print the sum of $a_s, a_{s+1}, ..., a_t$.

Note that the initial values of $a_i ( i = 0, 1, ..., n-1 )$ are 0.

Input

$n$ $q$
$query_1$
$query_2$
:
$query_q$

In the first line, $n$ (the number of elements in $A$) and $q$ (the number of queries) are given. Then, $i$-th query $query_i$ is given in the following format:

0 $s$ $t$ $x$

or

1 $s$ $t$

The first digit represents the type of the query. '0' denotes $update(s, t, x)$
and '1' denotes $find(s, t)$.

Output

For each $getSum$ query, print the sum in a line.

Constraints

$1 ≤ n ≤ 100000$

$1 ≤ q ≤ 100000$

$0 ≤ s ≤ t < n$

$-1000 ≤ x ≤ 1000$

Sample Input 1

6 7
0 1 3 1
0 2 4 -2
1 0 5
1 0 1
0 3 5 3
1 3 4
1 0 5

Sample Output 1

-5
1
6
8

Solution in C++14 (judge verdict: Accepted)

#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int INF = 1e9;
const ll LINF = 1e18;
template<class S,class T> ostream& operator << (ostream& out,const pair<S,T>& o){ out << "(" << o.first << "," << o.second << ")"; return out; }
template<class T> ostream& operator << (ostream& out,const vector<T> V){ for(int i = 0; i < V.size(); i++){ out << V[i]; if(i!=V.size()-1) out << " ";} return out; }
template<class T> ostream& operator << (ostream& out,const vector<vector<T> > Mat){ for(int i = 0; i < Mat.size(); i++) { if(i != 0) out << endl; out << Mat[i];} return out; }
template<class S,class T> ostream& operator << (ostream& out,const map<S,T> mp){ out << "{ "; for(auto it = mp.begin(); it != mp.end(); it++){ out << it->first << ":" << it->second; if(mp.size()-1 != distance(mp.begin(),it)) out << ", "; } out << " }"; return out; }


/*
 update(s,t,x): [s,t) をxに変更する。
 find(s,t): [s,t) の総和を出力する。
 */

const ll INIT = 0;
const ll NIL = LLONG_MAX;
struct SegTree {
    int N;
    ll init_v;
    vector<ll> node, lazy;
    
    SegTree(int _N):init_v(INIT) {
        N = 1;
        while (N < _N) N *= 2;
        node.resize(2 * N - 1, init_v);
        lazy.resize(2 * N - 1, NIL);
    }
    SegTree(int _N, vector<ll>& a){
        N = 1;
        while (N < _N) N *= 2;
        node.resize(2 * N - 1, init_v);
        lazy.resize(2 * N - 1, NIL);
        for(int i = 0; i < _N; i++){ node[i+N-1] = a[i]; }
        build();
    }
    void build(){ for(int k = N - 2; k >= 0; k--){ node[k] = node[2 * k + 1] + node[2 * k + 2];} }
    
    void lazy_evaluate(int k) {
        if (lazy[k] == NIL) return;
        node[k] = lazy[k];
        if (k < N - 1) {
            lazy[2 * k + 1] = lazy[k]/2;
            lazy[2 * k + 2] = lazy[k]/2;
        }
        lazy[k] = NIL;
    }
    
    /* [a,b) 引数の範囲に注意!! s~tまでを更新→update(s,t+1,~) */
    ll update(int a, int b, ll x) { return update(a, b, 0, 0, N, x); }
    ll update(int a, int b, int k, int l, int r, ll x) {
        if (r <= a || b <= l) {
            lazy_evaluate(k); // nodeの値を見るときは必ず遅延評価を更新する
            return node[k]; // updateでは全体の中の最小を見つける必要があるため, [l,r)外になっても値を参照
        }
        if (a <= l && r <= b) {
            lazy[k] = (r-l)*x;
            lazy_evaluate(k);
            return node[k];
        }
        else {
            lazy_evaluate(k);
            ll vl = update(a, b, 2 * k + 1, l, (l + r) / 2, x);
            ll vr = update(a, b, 2 * k + 2, (l + r) / 2, r, x);
            return node[k] = vl + vr;
        }
    }
    
    /* [a,b) 引数の範囲に注意!! */
    ll query(int a, int b) { return query(a, b, 0, 0, N); }
    ll query(int a, int b, int k, int l, int r) {
        if (r <= a || b <= l) return init_v;
        if (a <= l && r <= b) {
            lazy_evaluate(k);
            return node[k];
        }
        else {
            lazy_evaluate(k);
            ll vl = query(a, b, 2 * k + 1, l, (l + r) / 2);
            ll vr = query(a, b, 2 * k + 2, (l + r) / 2, r);
            return vl + vr;
        }
    }
};

int main(void) {
    cin.tie(0); ios_base::sync_with_stdio(false);
    int n,q; cin >> n >> q;
    SegTree seg(n);
    while(q--){
        int com; cin >> com;
        if(com == 0){
            int s,t,x; cin >> s >> t >> x;
            seg.update(s,t+1,x);
        }else{
            int s,t; cin >> s >> t;
            cout << seg.query(s,t+1) << endl;
        }
    }
    
    return 0;
}