Java中二叉树与斐波那契函数的示例分析

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题目一

解法

class Solution {    public int fib(int n) {        int[] arr = new int[31];        arr[0] = 0;        arr[1] = 1;        for(int i = 2;i<=n;i++){            arr[i] = arr[i-2]+arr[i-1];        }        return arr[n];    }}

题目二

解法

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode() {} *     TreeNode(int val) { this.val = val; } *     TreeNode(int val, TreeNode left, TreeNode right) { *         this.val = val; *         this.left = left; *         this.right = right; *     } * } */class Solution {    int index = 0;    int ans = 0;    public int kthSmallest(TreeNode root, int k) {        method(root,k);        return ans;    }    void method(TreeNode root, int k){        if(root==null) return;        method(root.left,k);        index++;        if(index==k){            ans = root.val;            return;        }        method(root.right,k);    }}

题目三

解法

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode() {} *     TreeNode(int val) { this.val = val; } *     TreeNode(int val, TreeNode left, TreeNode right) { *         this.val = val; *         this.left = left; *         this.right = right; *     } * } */class Solution {    public int minDepth(TreeNode root) {        if (root == null) {            return 0;        }        if (root.left == null && root.right == null) {            return 1;        }        int min_depth = Integer.MAX_VALUE;        if (root.left != null) {            min_depth = Math.min(minDepth(root.left), min_depth);        }        if (root.right != null) {            min_depth = Math.min(minDepth(root.right), min_depth);        }        return min_depth + 1;    }}

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