剑指Offer之Java算法习题精讲二叉搜索树与数组查找

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 {
  int ans;
  int pre;
  public int minDiffInBST(TreeNode root) {
      ans = Integer.MAX_VALUE;
      pre = -1;
      method(root);
      return ans;
  }
  public void method(TreeNode root){
      if(root==null) return;
      method(root.left);
      if(pre==-1){
          pre = root.val;
      }else{
          ans = Math.min(ans,root.val-pre);
          pre = root.val;
      }
      method(root.right); 
  }
}

 

题目二

 解法

class Solution {
  public int dominantIndex(int[] nums) {
      int f = Integer.MIN_VALUE;
      int fi = 0;
      int s = Integer.MIN_VALUE;
      int si = 0;
      for(int i = 0; i<nums.length;i++){
          if(nums[i]>f){
              s = f;
              f = nums[i];
              fi = i;
          }else if(nums[i]>s){
              s = nums[i];
          }
      }
      if(nums.length==1) return 0;
      if(2*s<=f) return fi;
      return -1; 
  }
}

 

题目三

解法

class Solution {
  public int repeatedNTimes(int[] nums) {
      int n = nums.length/2;
      HashMap<Integer,Integer> map =new HashMap<Integer,Integer>();
      for(int key : nums){
          if(map.containsKey(key)){
              map.put(key,map.get(key)+1);
              if(map.get(key)==n){
                  return key;
              }
          }else{
              map.put(key,1);
          }
      }
      return 0;
  }
}

 

 题目四

 解法

class Solution {
  public boolean uniqueOccurrences(int[] arr) {
      int[] nums = new int[2000];
      for(int i =0;i<arr.length;i++){
          nums[arr[i]+1000]+=1;
      }
      HashSet<Integer> set =new HashSet<Integer>();
      for(int i =0;i<nums.length;i++){
          if(nums[i]==0) continue;
          if(!set.add(nums[i])){
              return false;
          }else{
              set.add(nums[i]);
          }
      }
      return true;
  }
}

到此这篇关于剑指Offer之Java算法习题精讲二叉搜索树与数组查找的文章就介绍到这了,更多相关Java 二叉搜索树内容请搜索以前的文章或继续浏览下面的相关文章希望大家以后多多支持！

原文链接：https://blog.csdn.net/wai_58934/article/details/123336107

查看更多关于剑指Offer之Java算法习题精讲二叉搜索树与数组查找的详细内容...