面试编程题

记录面试的编程题

1. 二叉查找树的插入和查找

//二叉树定义
class TreeNode {
    int val;
    TreeNode left = null;
    TreeNode right = null;
    TreeNode() {
    }
    TreeNode(int val) {
        this.val = val;
    }
}

public class FindAndInsertTree01 {
	TreeNode root = null;
	
	//插入
	public void insert(TreeNode node) {
		if(root==null) {
			root=node;
		}else {
			TreeNode current = root;
			TreeNode parent = current;
			while(true) {
				parent=current;
				if(current.valvalue){
				current=current.left;
			}else {
				return current;
			}
			if(current==null)return null;
		}
		return null;
	}
}

2. 一个数二进制有多少个1

   public int NumberOf1(int n) {
    	int count=0;
    	if(n<0) {
    		count++;
    		n=n&0x7FFFFFFF;
    	}
    	while(n!=0) {
    		if(n%2!=0)count++;
    		n=n/2;
    	}
		return count;
    }

3. 0-n二进制一共有多少个1

4. 二分查找

	//非递归
	public int binSearch(int arr[],int k) {
		int low=0;
		int high=arr.length-1;
		while(lowk)high=middle-1;
			else low=middle+1;
		}
		return -1;
	}
	
	//递归
	public int binSearch(int arr[],int k,int low,int high) {
		if(lowk)binSearch(arr,k,low,middle-1);
			else binSearch(arr,k,middle+1,high);
		}
		return -1;
	}

5. 快速排序

	public int[] quickSort(int arr[],int low,int high) {
		if(low=temp) {
				high--;
			}
			arr[low]=arr[high];
			while(low

6. 反转链表

    public ListNode ReverseList(ListNode head) {
        ListNode next=null;
        ListNode pre=null;
        while(head!=null){
            next=head.next;
            head.next=pre;
            pre=head;
            head=next;
        }
        return pre;
    }

7. 二叉树前序遍历

	//递归
	public List postorder(TreeNode root) {
		List result=new ArrayList<>();
		postorder(root,result);
		return result;
	}
	private void postorder(TreeNode root, List result) {
		if(root==null)return;
		result.add(root.val);
		postorder(root.left,result);
		postorder(root.right,result);
	}
	
	//非递归
	public List postorderF(TreeNode root) {
		List result=new ArrayList<>();
		Stack s=new Stack<>();
		Stack temp=new Stack<>();
		TreeNode cur=root;
		while(!s.isEmpty()) {
			cur=s.pop();
			temp.add(cur);
			if(cur.left!=null)s.push(cur.left);
			if(cur.right!=null)s.push(cur.right);
		}
        while (!temp.isEmpty()) {
            cur = temp.pop();
            result.add(cur.val);
        }
		return result;
	}

8. 二叉树中序遍历

	//递归
	public List inorder(TreeNode root) {
		List result=new ArrayList<>();
		inorder(root,result);
		return result;
	}
	private void inorder(TreeNode root, List result) {
		if(root==null)return;
		inorder(root.left,result);
		result.add(root.val);
		inorder(root.right,result);
	}
	
	//非递归
	public List inorderF(TreeNode root) {
		List result=new ArrayList<>();
		Stack s=new Stack<>();
		s.push(root);
		TreeNode cur=root;
		while(cur != null ||!s.isEmpty()) {
			while(cur!=null) {
				s.push(cur.left);//添加根节点
				cur=cur.left;//添加左子节点
			}
			cur=s.pop();// 当前栈顶已经是最底层的左节点了，取出栈顶元素，访问该节点
			result.add(cur.val);
			cur=cur.right;// 添加右节点
		}
		return result;
	}

9. 二叉树后序遍历

	//递归
	public List postorder(TreeNode root) {
		List result=new ArrayList<>();
		postorder(root,result);
		return result;
	}
	private void postorder(TreeNode root, List result) {
		if(root==null)return;
		postorder(root.left,result);
		postorder(root.right,result);
		result.add(root.val);
	}
	
	//非递归
	public List postorderF(TreeNode root) {
		List result=new ArrayList<>();
		Stack s=new Stack<>();
		Stack temp=new Stack<>();
		TreeNode cur=root;
		while(!s.isEmpty()) {
			cur=s.pop();
			temp.add(cur);
			if(cur.left!=null)s.push(cur.left);
			if(cur.right!=null)s.push(cur.right);
		}
        while (!temp.isEmpty()) {
            cur = temp.pop();
            result.add(cur.val);
        }
		return result;
	}

二叉树的遍历 https://segmentfault.com/a/1190000016674584#articleHeader10

10. 合并排序的链表

	public ListNode Merge(ListNode list1,ListNode list2) {
		ListNode node=null;
		ListNode head=node;
		if(list1==null)return list2;
		if(list2==null)return list1;
		while(list1!=null&&list2!=null) {
			if(list1.val<=list2.val) {
				if(head==null) {
					head=node=list1;
				}else {
					node.next=list1;
					node=node.next;
				}
				list1=list1.next;
			}else {
				if(head==null) {
					head=node=list2;
				}else {
					node.next=list2;
					node=node.next;
				}
				list2=list2.next;
			}
		}
		if(list1==null) {
			node.next=list2;
		}else if(list2==null){
			node.next=list1;
		}
		return head;
	}

11.给一个数组和目标值，求数组中和为目标值的所有组合

     public int[] twoSum(int[] nums, int target) {
        Map map=new HashMap<>();
        for(int i=0;i

12.堆排序(最小K个数)

 public ArrayList GetLeastNumbers_Solution(int [] input, int k) {
    	ArrayList list=new ArrayList<>();
    if(input.length=0;i--) {
			sink(arr,i,N);
		}
		while(N>0) {
			swap(arr,0,N--);
			sink(arr,0,N);
		}
	}
	
	private static void sink(int[] arr, int i, int N) {
		while(2*i+1<=N) {
			int k=i*2+1;//左子树
			if(karr[k])break;
			swap(arr,i,k);
			i=k;
		}
	}

	private static void swap(int[] arr, int i, int k) {
		int temp=arr[i];
		arr[i]=arr[k];
		arr[k]=temp;
	}

13.最长公共子串

14.二叉树的深度