剑指Offer之Java算法习题精讲二叉树与斐波那契函数
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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