剑指Offer之Java算法习题精讲数组与二叉树
题目一
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 TreeNode sortedArrayToBST(int[] nums) { return method(nums,0,nums.length-1); } public TreeNode method(int[] nums,int lf,int rg){ if(lf>rg){ return null; } int mid = lf+(rg-lf)/2; TreeNode root = new TreeNode(nums[mid]); root.left = method(nums,lf,mid-1); root.right = method(nums,mid+1,rg); return root; } }
题目二
解法
class Solution { public boolean containsDuplicate(int[] nums) { HashSet<Integer> set = new HashSet<Integer>(); for(int i = 0;i<nums.length;i++){ if(!set.add(nums[i])){ return true; } set.add(nums[i]); } return false; } }
题目三
解法
class Solution { public boolean containsNearbyDuplicate(int[] nums, int k) { Map<Integer, Integer> map = new HashMap<Integer, Integer>(); int length = nums.length; for (int i = 0; i < length; i++) { int num = nums[i]; if (map.containsKey(num) && i - map.get(num) <= k) { return true; } map.put(num, i); } return false; } }
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