剑指Offer之Java算法习题精讲数组与二叉树

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;

http://* 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;

RYBwuHb * }

* }

*/

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) {

Hashhttp://Set set = new HashSet();

for(int i = 0;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 map = new HashMap();

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;

}

}

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 map = new HashMap();

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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