线段树的区间改变，基本板子。线段树学了一下午加一晚上，推荐一个大佬的博客，写的非常好:

#include 
     
      #include 
      
       #include 
       
        #include 
        
         using namespace std;const int maxn=100000+100;struct setree{    int val,am;}tree[maxn*3];int m,n;int a[maxn];void build(int root,int a[],int l,int r){    tree[root].am=0;    if(l==r)    {        tree[root].val=a[l];        return;    }    int mid=(l+r)/2;    build(root*2,a,l,mid);    build(root*2+1,a,mid+1,r);    tree[root].val=tree[root*2].val+tree[root*2+1].val;}void update(int root,int l,int r,int p,int q,int vval){    if(q
         
          r) return;    if(l>=p&&r<=q)    {        tree[root].val=vval*(r-l+1);        tree[root].am=vval;        return;    }    int mid=(l+r)/2;    int x=root;    if(tree[x].am)    {        tree[2*x].am=tree[x].am;//改了改延迟标记，使它等于要变成的数        tree[2*x+1].am=tree[x].am;        tree[2*x].val=tree[x].am*(mid-l+1);//区间的值等于区间长度乘以要变成的值        tree[2*x+1].val=tree[x].am*(r-mid);        tree[x].am=0;    }    update(root*2,l,mid,p,q,vval);    update(root*2+1,mid+1,r,p,q,vval);    tree[root].val=tree[root*2].val+tree[root*2+1].val;}int t;int main(){     scanf("%d",&t);    for(int zz=1;zz<=t;zz++)    {   scanf("%d",&n);       for(int i=1;i<=n;i++)          a[i]=1;         build(1,a,1,n);         scanf("%d",&m);      for(int i=1;i<=m;i++)      {          int aa,bb,cc;          scanf("%d%d%d",&aa,&bb,&cc);          update(1,1,n,aa,bb,cc);      }      printf("Case %d: The total value of the hook is %d.\n",zz,tree[1].val);    }    return 0;}
         
        
       
      
     

 

http://www.cnblogs.com/TenosDoIt/p/3453089.html