C语言 | 线段树

#include<stdio.h>
#define MAX_LEN 1000
void build_tree(int arr[],int tree[],int node,int start,int end)
{
	/*
		int arr[]:                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            y
		int tree[]:
		int node:树的根节点 
		int start:arr数组的 
		int end:arr数组的
	*/
	if(start==end)
	{
		tree[node] = arr[start];	
	} 
	else
	{
		int mid = (start+end)/2;
		int left_node = 2*node+1;
		int right_node = 2*node+2;
		
		build_tree(arr,tree,left_node,start,mid);
		build_tree(arr,tree,right_node,mid+1,end);
		tree[node] = tree[left_node]+tree[right_node]; 
	}
 } 
 
 void update_tree(int arr[],int tree[],int node,int start,int end,int idx,int val)
 {
 	/*
		 int idx:要更改的数在arr中的编号 
		 int val:要替换更改的数的值 
	 */
 	if(start==end)
 	{
	 	arr[idx] = val;
	 	tree[node]=val;
  	} 
  	else
  	{
	  	 int mid = (start+end)/2;
		 int left_node=2*node+1;
		 int right_node=2*node+2;
		 
		 //判断要改的数据落在了哪一个分支上 
		 if(idx >= start && idx <=mid)
		 {
		 	update_tree(arr,tree,left_node,start,mid,idx,val);
		 } 
		 else
		 {
		 	update_tree(arr,tree,right_node,mid+1,end,idx,val);
		 }
		 tree[node] = tree[left_node]+tree[right_node]; 
  	}
	
 }
int qury_tree(int arr[],int tree[],int node,int start,int end,int L,int R)
{
	//计算范围在L-R的和 
	printf("start = %d\n",start);
	printf("end = %d\n",end);
	printf("\n");
	if(R<start||L>end)
	{
		return 0;
	}
	else if(L<= start && end<=R)
	{
		return tree[node];
	}
	else if(start==end)
	{
		return tree[node];
	} 
	else
	{	
		int mid = (start+end)/2;
		int left_node=2*node+1;
	    int right_node=2*node+2;
	    int sum_left = qury_tree(arr,tree,left_node,start,mid,L,R);
	    int sum_right =  qury_tree(arr,tree,right_node,mid+1,end,L,R);
	    return  sum_left+sum_right;
	}
}
 int main()
 {
 	int arr[]={1,3,5,7,9,11};
 	int size = 6;
 	int tree[MAX_LEN] = {0};
 	
 	build_tree(arr,tree,0,0,size-1);
 	printf("create:\n");
 	int i;
 	for(i=0;i<15;++i)
 	{
 		printf("tree[%d] = %d\n",i,tree[i]);
	 }
	 
	printf("update:\n");
	update_tree(arr,tree,0,0,size - 1,4,6);
	for(i=0;i<15;++i)
 	{
 		printf("tree[%d] = %d\n",i,tree[i]);
	}
	
	printf("qury_tree:%d\n",qury_tree(arr,tree,0,0,size-1,2,5));
 	return 0;
 }