Minimum Absolute Difference in BST

最新推荐文章于 2018-01-11 15:22:31 发布

东邪岛主止水

最新推荐文章于 2018-01-11 15:22:31 发布

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本文介绍了一种算法问题的两种解决方案：一种是通过前序遍历寻找每个节点的最近邻居来计算二叉搜索树中任意两节点间的最小绝对差；另一种则是采用中序遍历，记录前一个节点值，以此找到最小绝对差。

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Given a binary search tree with non-negative values, find the minimum absolute difference between values of any two nodes.

Example:

Input:

1
\
3
/
2

Output:
1

Explanation:
The minimum absolute difference is 1, which is the difference between 2 and 1 (or between 2 and 3).

方法1：对每个节点进行寻找。前序遍历+寻找。

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {


public:
    int getMinimumDifference(TreeNode* root) {
        TreeNode * cur ;
        int left,right;

        // left
        cur = root -> left;
        if(cur){
            while(cur->right){
                cur = cur->right;
            }
            left = abs(cur->val - root->val);
        }
        else
            left = -1;

        // right
        cur = root -> right;
        if(cur){
            while(cur->left){
                cur = cur->left;
            }
            right = abs(cur->val - root->val);
        }
        else
            right = -1;

        int min_diff ;
        if(left == -1 || right == -1){
            if(left==-1 && right ==-1)
                min_diff = INT_MAX;
            else
                min_diff = (left==-1?right:left);
        }
        else{
            min_diff = min(left,right);
        }
        if(root->left)
            min_diff = min(min_diff,getMinimumDifference(root->left));
        if(root->right)
            min_diff = min(min_diff,getMinimumDifference(root->right));

        return min_diff;

    }
};

方法2：中序遍历，记录前一个节点。

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {

private:
    void traverse(TreeNode *root,int& last,int& diff){
            if(root->left)
                traverse(root->left,last,diff);
            if(last == -1)
                last = root -> val;
            else{
                 diff = min(diff,abs(last - root->val));
                 last = root -> val;
            }

            if(root->right)
                traverse(root->right,last,diff);

    }
public:
    int getMinimumDifference(TreeNode* root) {

        int diff = INT_MAX,last = -1;
        traverse(root,last,diff);
        return diff;
    }
};