线段树样例

线段树样例

#include<iostream>
using namespace std;

int a[100]={1,3,5,7,9,11};
int tree[1000]={0};
int n=6;

void built(int node,int start,int end) //node为树的根节号 start end
{
    if(start==end)
    {
        tree[node]=a[start];
    }
    else
    {
        int left_node  = node * 2 + 1;
        int right_node = 2 * node + 2;
        int mid=(start+end)/2;
        built(left_node,start,mid);
        built(right_node,mid+1,end);
        tree[node]=tree[left_node]+tree[right_node];
    }
}

int query(int node,int start,int end,int left,int right)
{
    if(start>right || end<left) return 0;
    else if(start==end) return tree[node];
    else if(start>=left && end<=right) return tree[node];

    int mid=(start+end)/2;
    int left_node  =node * 2 + 1;
    int right_node =node * 2 + 2;

    int left_sum  = query(left_node,start,mid,left,right);
    int right_sum = query(right_node,mid+1,end,left,right);
    return left_sum+right_sum;
}

void update_tree(int node ,int start,int end,int index,int value)//将index对应的值改为value
{
    if(start==end)
    {
        a[index]=value;
        tree[node]=value;
        return ;
    }
    int mid=(start+end)/2;
    int left_node  = node * 2 + 1;
    int right_node  = node * 2 + 2;
    if(index<=mid && index>=start) update_tree(left_node,start,mid,index,value);
    else update_tree(right_node,mid+1,end,index,value);
    tree[node]=tree[left_node]+tree[right_node];
}

int main()
{
    built(0,0,n-1);
    for(int i=0;i<2*n+2;i++)
        cout<<tree[i]<<endl;
    cout<<query(0,0,n-1,2,5)<<endl;
    update_tree(0,0,n-1,4,6);
    for(int i=0;i<2*n+2;i++)
        cout<<tree[i]<<endl;
    return 0;
}