京东笔试括号序列题 ac java版

这种组合的方法怎么证明是对的呢？虽然我大概理解了这个逻辑，但是有没有普适的定理什么的？楼主怎么想到这种组合方法的？

import java.util.Scanner; public class Main { public static void main(String[] args) { Scanner sc = new Scanner(System.in); String s = sc.next(); char[] c = s.toCharArray(); int count = 0; int temp = 0; int all = 1; for (int i = 0; i < c.length; i++) { if (c[i] == '(') { temp++; } else { if (temp > 1) { count = temp; temp = 0; int sum = 1; for (int j = count; j > 0; j--) { sum *= j; } all *= sum; } temp = 0; } } if (all == 0) { System.out.println(1); } else { System.out.println(all); } } } 不知错哪？

然后第二题暴力过了 import java.util.Scanner; public class Main { public static void main(String[] args) { Scanner sc = new Scanner(System.in); int left = sc.nextInt(); int right = sc.nextInt(); int time = 0; int[] ints = new int[10]; //避免频繁创建数组 for (int i = left; i <= right; i++) { if (isOk(ints, i)) { time++; } } System.out.println(time); } public static boolean isOk(int[] ints, int num) { int index = 0; while (num != 0) { ints[index++] = num % 10; num /= 10; } return isSumSame(0, 0, ints, 0, index); } private static boolean isSumSame(int sum1, int sum2, int[] ints, int i, int length) { if (i == length) { return sum1 == sum2; } return isSumSame(sum1, sum2 + ints[i], ints, i + 1, length) || isSumSame(sum1 + ints[i], sum2, ints, i + 1, length); } }

//好不容易 做出来一题，第二题始终20%。回家喂牛哦 public static void main(String[] args) { Scanner scanner = new Scanner(System.in); String str = scanner.nextLine(); List<Character> list = new ArrayList<>(); for (int i = 0; i < str.length(); i++) { list.add(str.charAt(i)); } int index = 1; int result = 1; while(!list.isEmpty()){ if (list.get(index)==')'){ result *= index; list.remove(index); list.remove(index-1); index = index-1; }else{ index++; } } System.out.println(result); }