LeetCode: Construct Binary Tree from Inorder and Postorder Traversal

思路:后序数组用来确定根节点的值和在数中的位置,中序数组用来确定左右子树的大小。代码细节参考了《剑指offer》一书中给的code,注意截断序列的时候不要分错。

class Solution {
public:
    TreeNode *buildTree(vector<int> &inorder, vector<int> &postorder) {
		TreeNode * root;
		int len = postorder.size();
		if(len < 1)return NULL;
		else
			root = constructTree(inorder.begin(),inorder.end()-1,postorder.begin(),postorder.end()-1);
		return root;
    }
	TreeNode * constructTree(vector<int>::iterator in_itbegin, vector<int>::iterator in_itend, 
		vector<int>::iterator post_itbegin, vector<int>::iterator post_itend){
			
			int v = *post_itend;
			TreeNode * root = new TreeNode(v);
			vector<int>::iterator p;
			for(p=in_itbegin; p<= in_itend;p++)
				if(*p == v)break;
			int leftlengh = p - in_itbegin, right_lengh = in_itend - p;
			if(leftlengh>0)
				root->left = constructTree(in_itbegin,p-1,post_itbegin,post_itend-right_lengh-1);
			if(right_lengh>0)
				root->right = constructTree(p+1,in_itend,post_itend-right_lengh+1,post_itend-1);
			return root;
	}
};


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