lintcode-线段树的构造-201

/**
* Definition of SegmentTreeNode:
* class SegmentTreeNode {
* public:
*     int start, end;
*     SegmentTreeNode *left, *right;
*     SegmentTreeNode(int start, int end) {
*         this->start = start, this->end = end;
*         this->left = this->right = NULL;
*     }
* }
*/
class Solution {
public:

SegmentTreeNode * build(int start, int end) {
if(start>end)
return nullptr;

SegmentTreeNode *root= new SegmentTreeNode(start,end);
if(start!=end){
int mid=start+(end-start)/2;
root->left=build(start,mid);
root->right=build(mid+1,end);
}
return root;
}
};