偷一下懒,复原ip坐半天给整怕了, 发现后两题10分钟一起AC,乐

93. 复原 IP 地址

 List<String> result = new ArrayList<String>();
    StringBuilder sb = new StringBuilder();


    /**
     * <A href="https://leetcode.cn/problems/restore-ip-addresses/"> 93.复原IP地址 </A>
     */
    public void backTracing(String s, int startIndex, int dotNum) {
        if (dotNum == 4 && sb.length() < s.length() + 4) {
            return;
        }
        if (dotNum == 4 && sb.length() == s.length() + 4) {
            result.add(sb.toString());
            return;
        }
        for (int i = startIndex; i < startIndex + 3 && i < s.length() && isValid(s, startIndex, i + 1); i++) {
            sb.append(s.substring(startIndex, i + 1));
            sb.append('.');
            dotNum++;
            backTracing(s, i + 1, dotNum);
            dotNum--;
            sb.delete(sb.length() - 1, sb.length()); // 移除点
            sb.delete(sb.length() - (i + 1 - startIndex), sb.length()); // 移数字
        }
    }


    public boolean isValid(String s, int startingIndex, int endIndex) {
        if (endIndex - startingIndex != 1 && s.charAt(startingIndex) == '0') {
            return false;
        }
        String d = s.substring(startingIndex, endIndex);
        return Integer.parseInt(d) >= 0 && Integer.parseInt(d) <= 255;
    }

这两题就很像,简单的我都不敢相信,我...

78. 子集

 LinkedList<Integer> path = new LinkedList<>();
    List<List<Integer>> res = new ArrayList<>();

    public List<List<Integer>> subsets(int[] nums) {
        backTracing(nums, 0);
        return res;
    }

    public void backTracing(int[] nums, int startIndex) {
        res.add(new ArrayList<>(path));
        for (int i = startIndex; i < nums.length; i++) {
            path.add(nums[i]);
            backTracing(nums, i + 1);
            path.removeLast();
        }
    }

90. 子集 II

LinkedList<Integer> path = new LinkedList<>();
    List<List<Integer>> res = new ArrayList<>();
    
    public List<List<Integer>> subsetsWithDup(int[] nums) {
        Arrays.sort(nums);
        backTracing2(nums, 0);
        return res;
    }

    public void backTracing2(int[] nums, int startIndex) {
        res.add(new ArrayList<>(path));

        for (int i = startIndex; i < nums.length; i++) {
            if (i > startIndex && nums[i] == nums[i - 1]) {
                continue;
            }
            path.add(nums[i]);
            backTracing2(nums, i + 1);
            path.removeLast();
        }
    }