线段树区间修改 lazy标记 大法

#include <cstdio>
#include <cstring>

#define maxn 100000 + 10
#define Lson L, mid, rt<<1
#define Rson mid+1, R, rt<<1|1

struct Node
{
    int sum, lazy;
} T[maxn<<2];

void PushUp(int rt)
{
    T[rt].sum = T[rt<<1].sum + T[rt<<1|1].sum;
}

void PushDown(int L, int R, int rt)
{
    int mid = (L + R) >> 1;
    T[rt<<1].sum = T[rt].lazy * (mid - L + 1);
    T[rt<<1|1].sum = T[rt].lazy * (R - mid);
    T[rt<<1].lazy = T[rt].lazy;
    T[rt<<1|1].lazy = T[rt].lazy;
    T[rt].lazy = 0;
}

void Build(int L, int R, int rt)
{
    if(L == R)
    {
        scanf("%d", &T[rt].sum);
        return ;
    }
    int mid = (L + R) >> 1;
    Build(Lson);
    Build(Rson);
    PushUp(rt);
}

void Update(int l, int r, int v, int L, int R, int rt)
{
    if(l==L && r==R)
    {
        T[rt].lazy = v;
        T[rt].sum = v * (R - L + 1);
        return ;
    }

    int mid = (L + R) >> 1;
    if(T[rt].lazy) PushDown(L, R, rt);

    if(r <= mid) Update(l, r, v, Lson);
    else if(l > mid) Update(l, r, v, Rson);
    else
    {
        Update(l, mid, v, Lson);
        Update(mid+1, r, v, Rson);
    }
    PushUp(rt);
}

int Query(int l, int r, int L, int R, int rt)
{
    if(l==L && r== R)
        return T[rt].sum;

    int mid = (L + R) >> 1;
    if(T[rt].lazy) PushDown(L, R, rt);

    if(r <= mid) return Query(l, r, Lson);
    else if(l > mid) return Query(l, r, Rson);
    return Query(l, mid, Lson) + Query(mid + 1, r, Rson);
}

int main()
{
    int n, q;
    scanf("%d", &n);
    Build(1, n, 1);
    scanf("%d", &q);
    int a, b, c, d;
    while(q--)
    {
        scanf("%d%d%d", &a, &b, &c);
        if(a)
        {
            scanf("%d", &d);
            Update(b, c, d, 1, n, 1);
        }
        else printf("%d\n", Query(b, c, 1, n, 1));
    }

    return 0;
}