C++ solution--counting numbers of left tree


  • 4
    S

    class Solution {

    public:

    int kthSmallest(TreeNode* root, int k) {
        if (!root) return 0;
        if (k==0) return root->val;
        
        int n=count_size(root->left);
        if (k==n+1) return root->val;
        
        if (n>=k){
            return kthSmallest(root->left, k);
        }
        if (n<k){
            return kthSmallest(root->right, k-n-1);
        }
        
    }
    
    int count_size(TreeNode* root){
        if (!root) return 0;
        return 1+count_size(root->left)+count_size(root->right);
        
    }
    

    };


  • 0
    V

    @sophie2509 In this, size of sub-trees are computed repeatedly which is slow. Rather, go inorder(bottom-up for left sub tree and top-down for right sub tree) and whenever size equals k, return the node.


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