{"id":19028122,"url":"https://github.com/ffcactus/leetcode-java","last_synced_at":"2025-07-29T16:43:59.063Z","repository":{"id":127618565,"uuid":"375718441","full_name":"ffcactus/leetcode-java","owner":"ffcactus","description":null,"archived":false,"fork":false,"pushed_at":"2022-10-03T11:17:33.000Z","size":51,"stargazers_count":0,"open_issues_count":0,"forks_count":0,"subscribers_count":2,"default_branch":"master","last_synced_at":"2025-02-21T19:44:53.363Z","etag":null,"topics":[],"latest_commit_sha":null,"homepage":null,"language":"Java","has_issues":true,"has_wiki":null,"has_pages":null,"mirror_url":null,"source_name":null,"license":null,"status":null,"scm":"git","pull_requests_enabled":true,"icon_url":"https://github.com/ffcactus.png","metadata":{"files":{"readme":"README.md","changelog":null,"contributing":null,"funding":null,"license":null,"code_of_conduct":null,"threat_model":null,"audit":null,"citation":null,"codeowners":null,"security":null,"support":null,"governance":null,"roadmap":null,"authors":null,"dei":null,"publiccode":null,"codemeta":null}},"created_at":"2021-06-10T14:04:01.000Z","updated_at":"2022-09-24T10:59:15.000Z","dependencies_parsed_at":"2023-07-09T09:02:19.377Z","dependency_job_id":null,"html_url":"https://github.com/ffcactus/leetcode-java","commit_stats":null,"previous_names":[],"tags_count":0,"template":false,"template_full_name":null,"purl":"pkg:github/ffcactus/leetcode-java","repository_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/ffcactus%2Fleetcode-java","tags_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/ffcactus%2Fleetcode-java/tags","releases_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/ffcactus%2Fleetcode-java/releases","manifests_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/ffcactus%2Fleetcode-java/manifests","owner_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/owners/ffcactus","download_url":"https://codeload.github.com/ffcactus/leetcode-java/tar.gz/refs/heads/master","sbom_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/ffcactus%2Fleetcode-java/sbom","host":{"name":"GitHub","url":"https://github.com","kind":"github","repositories_count":267718973,"owners_count":24133466,"icon_url":"https://github.com/github.png","version":null,"created_at":"2022-05-30T11:31:42.601Z","updated_at":"2022-07-04T15:15:14.044Z","status":"online","status_checked_at":"2025-07-29T02:00:12.549Z","response_time":2574,"last_error":null,"robots_txt_status":"success","robots_txt_updated_at":"2025-07-24T06:49:26.215Z","robots_txt_url":"https://github.com/robots.txt","online":true,"can_crawl_api":true,"host_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub","repositories_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories","repository_names_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repository_names","owners_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/owners"}},"keywords":[],"created_at":"2024-11-08T21:10:00.490Z","updated_at":"2025-07-29T16:43:59.046Z","avatar_url":"https://github.com/ffcactus.png","language":"Java","funding_links":[],"categories":[],"sub_categories":[],"readme":"# leetcode-java\n\n# Backtracking\nBacktracking is a kind of BFS.\nThe helper function has the following form.\n```java\nvoid backtracking(参数) {\n    if (终止条件) {\n        存放结果;\n        return;\n    }\n\n    for (选择：本层集合中元素（树中节点孩子的数量就是集合的大小）) {\n        处理节点;\n        backtracking(路径，选择列表); // 递归\n        回溯，撤销处理结果\n    }\n}\n```\n## Typical questions\n1. Given 4 numbers, find all the solutions that using them to form a time expression.\n   For example give your [1,2,3,4], the time expression can be 12:34, 12:43, 13:24, 13:42 and etc.\n   Here is the feature to this question:\n   * A solution need includes all the inputs.\n   * Permutation problem\n2. Give your a number string, for example \"123345\" find out all the possible IPv4 expression.\n   For example, it can be \"12.33.45\", \"123.3.45\", \"1.233.4.5\" and etc.\n   Here is the feature to this question:\n   * A solution must follow the order to the input.","project_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fffcactus%2Fleetcode-java","html_url":"https://awesome.ecosyste.ms/projects/github.com%2Fffcactus%2Fleetcode-java","lists_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fffcactus%2Fleetcode-java/lists"}