NC_45_THREE_ORDERS NC_46_TARGET_VALUE

package org.example.interview.practice;

import java.util.ArrayList;

/**
 * @author xianzhe.ma
 * @date 2021/8/30
 */

public class NC_45_THREE_ORDERS {

    public static int[][] threeOrders(TreeNode root) {
        // write code here
        ArrayList<TreeNode> list1 = new ArrayList<>();
        ArrayList<TreeNode> list2 = new ArrayList<>();
        ArrayList<TreeNode> list3 = new ArrayList<>();

        preOrder(root, list1);
        midOrder(root, list2);
        postOrder(root, list3);

        int[][] ret = new int[3][list1.size()];
        int[] pre = new int[list1.size()];
        int[] mid = new int[list1.size()];
        int[] post = new int[list1.size()];
        int index = 0;
        for (TreeNode node : list1) {
            pre[index++] = node.val;
        }
        index = 0;
        for (TreeNode node : list2) {
            mid[index++] = node.val;
        }
        index = 0;
        for (TreeNode node : list3) {
            post[index++] = node.val;
        }
//        System.arraycopy();
        for (int j = 0; j < list1.size(); j++) {
            ret[0][j] = pre[j];
        }

        for (int j = 0; j < list1.size(); j++) {
            ret[1][j] = mid[j];
        }

        for (int j = 0; j < list1.size(); j++) {
            ret[2][j] = post[j];
        }

        return ret;
    }

    private static ArrayList<TreeNode> preOrder(TreeNode root, ArrayList<TreeNode> list) {
        if (root == null) {
            return list;
        }
        list.add(root);
        preOrder(root.left, list);
        preOrder(root.right, list);
        return list;
    }

    private static ArrayList midOrder(TreeNode root, ArrayList list) {
        if (root == null) {
            return list;
        }
        midOrder(root.left, list);
        list.add(root);
        midOrder(root.right, list);
        return list;
    }

    private static ArrayList postOrder(TreeNode root, ArrayList list) {
        if (root == null) {
            return list;
        }
        postOrder(root.left, list);
        postOrder(root.right, list);
        list.add(root);
        return list;
    }

    public static class TreeNode {
        int val = 0;
        TreeNode left = null;
        TreeNode right = null;

        public TreeNode(int val) {
            this.val = val;
        }
    }

    public static void main(String[] args) {
        TreeNode node1 = new TreeNode(1);
        TreeNode node2 = new TreeNode(2);
        TreeNode node3 = new TreeNode(3);

        node1.left = node2;
        node1.right = node3;

        threeOrders(node1);
    }
}

package org.example.interview.practice;

/**
 * @author xianzhe.ma
 * @date 2021/11/6
 */

import java.util.*;

public class NC_46_TARGET_VALUE {

    public static ArrayList<ArrayList<Integer>> combinationSum2(int[] num, int target) {
        ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
        ArrayList<Integer> arr = new ArrayList<Integer>();
        if (num == null || num.length == 0 || target < 0) return res;
        Arrays.sort(num);//对候选数组进行排序 方便后续处理
        dfs(num, target, res, arr, 0);
        return res;
    }

    public static void dfs(int[] num, int target, ArrayList<ArrayList<Integer>> res, ArrayList<Integer> arr, int start) {
        if (target == 0) {
            //已找到一组 存储进res
            res.add(new ArrayList<Integer>(arr));
            return;
        }
        if (start >= num.length) return;
        for (int i = start; i < num.length; i++) {
            if (i > start && num[i] == num[i - 1])
                continue;
            //回溯操作
            if (num[i] <= target) {
                arr.add(num[i]);
                dfs(num, target - num[i], res, arr, i + 1);
                arr.remove(arr.size() - 1);
            }
        }
        return;
    }

    public static void main(String[] args) {
        int[] array = {2, 3};
        combinationSum2(array, 5);
    }
}