线段树——E

In the game of DotA, Pudge’s meat hook is actually the most horrible thing for most of the heroes. The hook is made up of several consecutive metallic sticks which are of the same length. 

Now Pudge wants to do some operations on the hook. 

Let us number the consecutive metallic sticks of the hook from 1 to N. For each operation, Pudge can change the consecutive metallic sticks, numbered from X to Y, into cupreous sticks, silver sticks or golden sticks. 
The total value of the hook is calculated as the sum of values of N metallic sticks. More precisely, the value for each kind of stick is calculated as follows: 

For each cupreous stick, the value is 1. 
For each silver stick, the value is 2. 
For each golden stick, the value is 3. 

Pudge wants to know the total value of the hook after performing the operations. 
You may consider the original hook is made up of cupreous sticks. 

Input

The input consists of several test cases. The first line of the input is the number of the cases. There are no more than 10 cases. 
For each case, the first line contains an integer N, 1<=N<=100,000, which is the number of the sticks of Pudge’s meat hook and the second line contains an integer Q, 0<=Q<=100,000, which is the number of the operations. 
Next Q lines, each line contains three integers X, Y, 1<=X<=Y<=N, Z, 1<=Z<=3, which defines an operation: change the sticks numbered from X to Y into the metal kind Z, 

不多说，初始化，看代码

#include <iostream>
#include <cstdio>
using namespace std;
#define N 500000
int lazy[N];
int sum[N];
void build(int l,int r,int rt){
    sum[rt]=1;
    lazy[rt]=0;//必须在这里初始化？？？
    if(l==r) {
        return;
    }
    int mid=(l+r)/2;
    build(l,mid,rt*2);
    build(mid+1,r,rt*2+1);
    sum[rt]=sum[rt*2]+sum[rt*2+1];
}
void pushdown(int l,int r,int rt){
    if(lazy[rt]){
        lazy[rt*2]=lazy[rt];
        lazy[rt*2+1]=lazy[rt];
        sum[rt*2]=lazy[rt]*l;
        sum[rt*2+1]=lazy[rt]*r;
        lazy[rt]=0;
    }
}
void update(int l1,int r1,int v,int l,int r,int rt){
    if(l1<=l&&r1>=r){
        sum[rt]=v*(r-l+1);
        lazy[rt]=v;
        return;
    }
    int mid=(l+r)/2;
    pushdown(mid-l+1,r-mid,rt);
    if(l1<=mid){
        update(l1,r1,v,l,mid,rt*2);
    }
    if(r1>mid){
        update(l1,r1,v,mid+1,r,rt*2+1);
    }
    sum[rt]=sum[rt*2]+sum[rt*2+1];
}
int main()
{
    int t,cnt=0,n,q;
    scanf("%d",&t);
    while(t--){
        cnt++;
        scanf("%d",&n);
        build(1,n,1);
        scanf("%d",&q);
        while(q--){
            int x,y,z;
            scanf("%d%d%d",&x,&y,&z);
            update(x,y,z,1,n,1);
        }
         printf("Case %d: The total value of the hook is %d.
", cnt, sum[1]);
    }
    return 0;
}