hihoCoder 1078 线段树的区间修改

<pre name="code" class="cpp">#include <iostream>
#include <cstdio>
#include <cstring>
#define N 100005
using namespace std;

struct node{
    int l,r,sum;
    int sett;
}tree[N<<2];
int a
;
int ans;

void build(int m,int l,int r){
    tree[m].l = l;
    tree[m].r = r;
    tree[m].sett = -1;
    if(l == r){
        tree[m].sum = a[l];
        return;
    }
    int mid = (l+r)>>1;
    build(m<<1,l,mid);
    build((m<<1)+1,mid+1,r);
    tree[m].sum = tree[m<<1].sum + tree[(m<<1)+1].sum;
}

void pushdown(int m){
    if(tree[m].l >= tree[m].r)
        return;
    if(tree[m].sett != -1){
        tree[m<<1].sett = tree[(m<<1)+1].sett = tree[m].sett;
        tree[m<<1].sum = (tree[m<<1].r-tree[m<<1].l+1)*tree[m].sett;
        tree[(m<<1)+1].sum = (tree[(m<<1)+1].r-tree[(m<<1)+1].l+1)*tree[m].sett;
        tree[m].sett = -1;
    }
}

void maintain(int m){
    tree[m].sum = tree[m<<1].sum + tree[(m<<1)+1].sum;
}

void update(int m,int l,int r,int val){
    if(tree[m].l >= l && tree[m].r <= r){
        tree[m].sett = val;
        tree[m].sum = (tree[m].r-tree[m].l+1)*val;
        return;
    }
    pushdown(m);
    int mid = (tree[m].l+tree[m].r)>>1;
    if(l <= mid)
        update(m<<1,l,r,val);
    if(mid < r)
        update((m<<1)+1,l,r,val);
    maintain(m);
}

void query(int m,int l,int r){
    if(tree[m].l >= l && tree[m].r <= r){
        ans += tree[m].sum;
        return;
    }
    pushdown(m);
    int mid = (tree[m].l+tree[m].r)>>1;
    if(l <= mid)
        query(m<<1,l,r);
    if(mid < r)
        query(m<<1|1,l,r);
    maintain(m);
}

int main(){
    int n,m;
    while(~scanf("%d",&n)){
        for(int i = 1; i <= n; i++)
            scanf("%d",&a[i]);
        build(1,1,n);
        scanf("%d",&m);
        int op,a,b,c;
        for(int i = 1; i <= m; i++){
            scanf("%d",&op);
            if(op == 0){
                ans = 0;
                scanf("%d%d",&a,&b);
                query(1,a,b);
                printf("%d\n",ans);
            }
            else{
                scanf("%d%d%d",&a,&b,&c);
                update(1,a,b,c);
            }
        }
    }
    return 0;
}