题目1

使用 StringBuilder 模拟栈的行为，通过判断相邻2个字符是否相同，如果相同就进行删除

public class Main {public static String fun(String s) {if (s == null || s.length() <= 1) return s;StringBuilder builder = new StringBuilder(); // 使用StringBuilder模拟栈for (char c : s.toCharArray()) {if (builder.length() > 0 && builder.charAt(builder.length() - 1) == c) {builder.deleteCharAt(builder.length() - 1);} else {builder.append(c);}}return builder.toString();}public static void main(String[] args) {Scanner scanner = new Scanner(System.in);String s = scanner.nextLine();System.out.println(fun(s));}
}

题目2

public class Main {public static int climbStairs(int n) {if (n <= 2) {return n;}int[] dp = new int[n + 1]; // 动态规划数组dp[1] = 1;dp[2] = 2;for (int i = 3; i <= n; i++) {dp[i] = dp[i - 1] + dp[i - 2]; // 状态转移方程}return dp[n];}public static void main(String[] args) {Scanner scanner = new Scanner(System.in);int n = scanner.nextInt();System.out.println(climbStairs(n));}
}

题目3

 public class Main {public static void main(String[] args) {Scanner scanner = new Scanner(System.in);int N = scanner.nextInt();int n = N;ArrayList<Integer> list = new ArrayList<>(N);while (n > 0) {list.add(scanner.nextInt());n -= 1;}ArrayList<Integer> list1 = new ArrayList<>(N);for (int i = 0; i < N; i++) {list1.add(0);}int res = 0;// 每次从每个口袋中取列表中最小值个糖果（0不管）while (!list1.equals(list)) {int min = Integer.MAX_VALUE;for (Integer i : list) {if (i == 0) continue;if (i < min) min = i;}for (int i = 0; i < list.size(); i++) {if (list.get(i) == 0) continue;list.set(i, list.get(i) - min);}res+=1;}System.out.println(res);}
}

题目4

输入示例：

5
1 -2 3 -4 5

输出示例：

15

思路很简单，但是当时做题提交的时候，通过率总是18%。不知道为啥，后面我改成了Long类型，然后就通过了全部用例。（易错1：第一次提交没考虑0的情况）

// 这个是笔试通过的代码 当然优化之处很多
public class Main {public static void main(String[] args) {Scanner scanner = new Scanner(System.in);int N = scanner.nextInt();int n = N;ArrayList<Long> list = new ArrayList<>(N);while (n > 0) {list.add(scanner.nextLong());n -= 1;}if (list.size() == 1) {System.out.println(list.get(0));return;}int cnt = 0;// 统计负数个数（0也算入）int zero = 0;for (Long i : list) {if (i == 0) zero = 1;if (i <= 0) {cnt += 1;}}Long res = 0L;Long min = Long.MAX_VALUE;for (Long i : list) {res += Math.abs(i);if (min > Math.abs(i)) min = Math.abs(i);}if (zero != 0) {System.out.println(res);return;}if ((cnt & 1) == 1) {// 奇数个负数res = res - min - min;}System.out.println(res);}
}