代码随想录算法训练营第二十九天| 93.复原IP地址-优快云博客

本文链接：https://blog.youkuaiyun.com/m0_37767445/article/details/135739091

文章介绍了两个编程问题的解决方案：一个是如何通过深度优先搜索(DFS)恢复有效IP地址，另一个是如何生成整数数组的子集，包括去重版本。作者提供了Java代码实现这两个算法

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93.复原 IP 地址

public List<String> restoreIpAddresses(String s) {
    if (s.length() > 12|| "000256".equals(s)) {
        return new ArrayList<>();
    }
    List<String> path = new ArrayList<>();
    List<List<String>> ans = new ArrayList<>();
    char[] chars = s.toCharArray();
    dfs1(s, chars, 0, path, ans);
    List<String> res = new ArrayList<>();
    for (List<String> an : ans) {
        StringBuffer stringBuffer = new StringBuffer();
        for (int i = 0; i < an.size(); i++) {
            if (i == an.size() - 1) {
                stringBuffer.append(an.get(i));
                break;
            }
            stringBuffer.append(an.get(i) + ".");
        }
        res.add(stringBuffer.toString());
    }

    return res;
}

public void dfs1(String s, char[] nums, int index, List<String> path, List<List<String>> ans) {

    if (index == nums.length && path.size() == 4) {
        ans.add(new ArrayList<>(path));
        return;
    }
    if (index > nums.length) {
        return;
    }

    for (int i = index; i < nums.length; i++) {
        if (isValidIp(s, nums, index, i)) {
            String substring = s.substring(index, i + 1);
            path.add(substring);
            dfs1(s, nums, i + 1, path, ans);
            path.remove(path.size() - 1);
        }
    }

}

public Boolean isValidIp(String s, char[] chars, int head, int tail) {
    String substring = s.substring(head, tail + 1);

    if (!"".equals(substring)) {
        Long integer = Long.valueOf(substring);
        if (integer > 256) {
            return false;
        }
    }

    if (tail - head > 3) {
        return false;
    }
    if (chars[head] == '0' && tail != head) {
        return false;
    }
    return true;

}

78.子集

public static List<List<Integer>> subsets(int[] nums) {
    //子集 对答案的长度没有要求 第一种方式 从上往下遍历
    List<Integer> path = new ArrayList<>();
    List<List<Integer>> ans = new ArrayList<>();
    dfs(nums, 0, path, ans);
    return ans;

}

public static void dfs(int[] nums, int index, List<Integer> path, List<List<Integer>> ans) {
    ans.add(new ArrayList<>());

    for (Integer integer : path) {
        ans.get(ans.size() - 1).add(integer);
    }
    if (index >= nums.length) {
        return;
    }
    for (int i = index; i < nums.length; i++) {
        path.add(nums[i]);
        dfs(nums, i+1, path, ans);
        path.remove(path.size() - 1);
    }

}

90.子集II

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

public static void dfs(int[] nums, int index, List<Integer> path, List<List<Integer>> ans) {
    if (!ans.contains(path)) {
        ans.add(new ArrayList<>());
        for (Integer integer : path) {
            ans.get(ans.size() - 1).add(integer);
        }
        if (index >= nums.length) {
            return;
        }
    }


    for (int i = index; i < nums.length; i++) {
        path.add(nums[i]);
        dfs(nums, i + 1, path, ans);
        path.remove(path.size() - 1);
    }

}