遇到5个面试题,要求一个小时,结果花了一天

5个问题
问题1:使用for循环、while循环和递归写出3个函数来计算给定数列的总和。
问题2:编写一个交错合并列表元素的函数。例如：给定的两个列表为[a，B，C]和[1，2，3]，函数返回[a，1，B，2，C，3]。
问题3:编写一个计算前100位斐波那契数的函数。根据定义，斐波那契序列的前两位数字是0和1，随后的每个数字是前两个数字的和。例如，前10位斐波那契数为：0，1，1，2，3，5，8，13，21，34。
问题4:编写一个能将给定非负整数列表中的数字排列成最大数字的函数。例如，给定[50，2，1,9]，最大数字为95021。
问题5:编写一个在1，2，…，9（顺序不能变）数字之间插入+或-或什么都不插入，使得计算结果总是100的程序，并输出所有的可能性。
例如：1 + 2 + 34–5 + 67–8 + 9 = 100。

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.Optional;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.Supplier;
import java.util.stream.Stream;

public class One2Five {

	public void one() {
		int[] arr = { 1, 2, 4, 3, 0, 1, 2, 3 };
		int sum = 0;
		for (int i : arr) {
			sum += i;
		}
		System.out.println("sum=" + sum);
		sum = 0;
		int i = 0;
		while (i < arr.length) {
			sum += arr[i++];
		}
		System.out.println("sum=" + sum);
		sum = 0;
		sum = sum(arr, 0);
		System.out.println("sum=" + sum);
	}

	private int sum(int[] arr, int i) {
		if (i == arr.length)
			return 0;
		return arr[i] + sum(arr, i + 1);
	}

	public void two() {
		int[] b = { 0, 2, 4, 6, 8 };
		int[] a = { 1, 3, 5, 7, 9 };
		int[] c = new int[a.length + b.length];

		int bx = 0;
		int ax = 0;
		boolean f = true;

		boolean bof = false;
		boolean aof = false;
		for (int i = 0; i < c.length; i++) {
			if (f && !bof) {
				if (bx < b.length) {
					c[i] = b[bx++];
				} else
					bof = true;
				f = false;
			} else if (!aof) {
				if (ax < a.length) {
					c[i] = a[ax++];
				} else
					aof = true;
				f = true;
			}
		}

		for (int i : c) {
			System.out.print(i + ",");
		}
	}

	public long fboi(int n) {
		if (n == 1)
			return 0;
		if (n == 2)
			return 1;
		long r = fboi(n - 1) + fboi(n - 2);
		return r;
	}

	public void three() {
		long all = fboi(10);
		System.out.println(all);
	}

	public static Stream<Integer> range(final Integer start, Integer length, Integer step, List<Integer> except) {
		Supplier<Integer> seed = new Supplier<Integer>() {

			private Integer next = start;

			@Override
			public Integer get() {
				Integer _next = next;
				next += step;
				return _next;
			}
		};
		return Stream.generate(seed).limit(length).filter(new Predicate<Integer>() {
			@Override
			public boolean test(Integer t) {
				if (except == null)
					return true;
				if (except.contains(t))
					return false;
				return true;
			}
		});
	}

	List<Integer> list = new ArrayList<Integer>();
	AtomicInteger count = new AtomicInteger(0);
	List<List<Integer>> WholeArrangementList = new ArrayList<>();

	public void WholeArrangement(int N) {
		Stream<Integer> range = range(0, N, 1, list);
		range.forEach(new Consumer<Integer>() {
			@Override
			public void accept(Integer t) {
				list.add(t);
				WholeArrangement(N);
				list.remove(list.size() - 1);
			}
		});
		if (list.size() == N) {
			count.incrementAndGet();
			List<Integer> arrangement = new ArrayList<Integer>(list);
			WholeArrangementList.add(arrangement);
			System.out.println(Arrays.toString(list.toArray()));
		}
	}

	public void four() {
		Integer[] arr = { 89, 12, 43, 23, 1, 8 };
		WholeArrangement(arr.length);

		Stream<String> sorted = WholeArrangementList.stream().map(new Function<List<Integer>, String>() {
			@Override
			public String apply(List<Integer> t) {
				StringBuffer sf = new StringBuffer();
				for (Integer idx : t) {
					sf.append(arr[idx]);
				}
				return sf.toString();
			}
		}).sorted(Comparator.reverseOrder());
		sorted.onClose(new Runnable() {
			@Override
			public void run() {
				Optional<String> findFirst = sorted.findFirst();
				System.out.println(findFirst.get());
			}
		});

		Object[] array = sorted.toArray();
		Stream.of(array).forEach(new Consumer<Object>() {
			@Override
			public void accept(Object t) {
				System.out.println(t);
			}
		});

		System.out.println("___________________________________________________max");
		Optional<Object> findFirst = Stream.of(array).findFirst();
		System.out.println(findFirst.get());
	}

	
	char[] operator = { ' ', '+', '-' };
	int[] nums = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
	List<Character> operatorList = new ArrayList<Character>();

	private int joinNumCalc() {
		int joinNum = 0;
		char preOperate = 'S';// 模拟个开始符
		int index = operatorList.size() - 1;
		int count = 1;

		if (operatorList.size() <= 1)
			return 0;
		if (operatorList.get(index) == ' ')
			return 0;

		for (int i = index - 1; i >= 0; i--) {
			if (operatorList.get(i) == ' ') {
				count++;
			} else {
				preOperate = operatorList.get(i);
				break;
			}
		}
		if (preOperate == 'S') {
			count = count - 1;
		}
		for (int i = index - count; i < index; i++) {
			joinNum = joinNum * 10 + nums[i];
		}

		switch (preOperate) {
		case '+':
			return joinNum;
		case '-':
			return -joinNum;
		case 'S':
			return joinNum;
		default:
			break;
		}
		return 0;
	}

	public void exp_calc(int value) {
		if (operatorList.size() == nums.length) {
			count.incrementAndGet();
			operatorList.add('E');// 加一个结束符
			value = value + joinNumCalc();
			operatorList.remove(operatorList.size() - 1);
			if (value == 100) {
				for (int i = 0; i < operatorList.size(); i++) {
					Character operate = operatorList.get(i);
					switch (operate) {
					case '+':

					case '-':
						if (i == 0 && operate == '+') {
						} else {
							System.out.print(operate);
						}
						System.out.print(nums[i]);
						break;
					case ' ':
						System.out.print(nums[i]);
					default:
						break;
					}
				}
				System.out.println();
				// System.out.println("value = " + value + "\t" +
				// Arrays.toString(operatorList.toArray(new Character[0])));
			}

			return;
		}
		for (int i = 0; i < operator.length; i++) {
			if (operatorList.size() == 0 && operator[i] == ' ')
				continue;
			operatorList.add(operator[i]);
			int valueAdd = value + joinNumCalc();
			exp_calc(valueAdd);
			operatorList.remove(operatorList.size() - 1);
		}
	}

	public void five() {
		exp_calc(0);
		System.out.println(count);
	}

	public static void main(String[] args) {
		One2Five five = new One2Five();
		five.one();
		five.two();
		five.three();
		five.four();
		five.five();
	}

}