剑指Offer之Java算法习题精讲二叉树与斐波那契函数剑指Offer之Java算法习题精讲二

题目一
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【剑指Offer之Java算法习题精讲二叉树与斐波那契函数】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

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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

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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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