--- title: 2.08 ✅ Backtracking type: docs weight: 8 --- # Backtracking ![](https://img.halfrost.com/Leetcode/Backtracking.png) - 排列问题 Permutations。第 46 题，第 47 题。第 60 题，第 526 题，第 996 题。 - 组合问题 Combination。第 39 题，第 40 题，第 77 题，第 216 题。 - 排列和组合杂交问题。第 1079 题。 - N 皇后终极解法(二进制解法)。第 51 题，第 52 题。 - 数独问题。第 37 题。 - 四个方向搜索。第 79 题，第 212 题，第 980 题。 - 子集合问题。第 78 题，第 90 题。 - Trie。第 208 题，第 211 题。 - BFS 优化。第 126 题，第 127 题。 - DFS 模板。(只是一个例子，不对应任何题) ```go func combinationSum2(candidates []int, target int) [][]int { if len(candidates) == 0 { return [][]int{} } c, res := []int{}, [][]int{} sort.Ints(candidates) findcombinationSum2(candidates, target, 0, c, &res) return res } func findcombinationSum2(nums []int, target, index int, c []int, res *[][]int) { if target == 0 { b := make([]int, len(c)) copy(b, c) *res = append(*res, b) return } for i := index; i < len(nums); i++ { if i > index && nums[i] == nums[i-1] { // 这里是去重的关键逻辑 continue } if target >= nums[i] { c = append(c, nums[i]) findcombinationSum2(nums, target-nums[i], i+1, c, res) c = c[:len(c)-1] } } } ``` - BFS 模板。(只是一个例子，不对应任何题) ```go func updateMatrix_BFS(matrix [][]int) [][]int { res := make([][]int, len(matrix)) if len(matrix) == 0 || len(matrix[0]) == 0 { return res } queue := make([][]int, 0) for i, _ := range matrix { res[i] = make([]int, len(matrix[0])) for j, _ := range res[i] { if matrix[i][j] == 0 { res[i][j] = -1 queue = append(queue, []int{i, j}) } } } level := 1 for len(queue) > 0 { size := len(queue) for size > 0 { size -= 1 node := queue[0] queue = queue[1:] i, j := node[0], node[1] for _, direction := range [][]int{{-1, 0}, {1, 0}, {0, 1}, {0, -1}} { x := i + direction[0] y := j + direction[1] if x < 0 || x >= len(matrix) || y < 0 || y >= len(matrix[0]) || res[x][y] < 0 || res[x][y] > 0 { continue } res[x][y] = level queue = append(queue, []int{x, y}) } } level++ } for i, row := range res { for j, cell := range row { if cell == -1 { res[i][j] = 0 } } } return res } ``` | No. | Title | Solution | Difficulty | TimeComplexity | SpaceComplexity |Favorite| Acceptance | |:--------:|:------- | :--------: | :----------: | :----: | :-----: | :-----: |:-----: | |0017|Letter Combinations of a Phone Number|[Go]({{< relref "/ChapterFour/0001~0099/0017.Letter-Combinations-of-a-Phone-Number.md" >}})|Medium| O(log n)| O(1)||50.5%| |0022|Generate Parentheses|[Go]({{< relref "/ChapterFour/0001~0099/0022.Generate-Parentheses.md" >}})|Medium| O(log n)| O(1)||66.8%| |0037|Sudoku Solver|[Go]({{< relref "/ChapterFour/0001~0099/0037.Sudoku-Solver.md" >}})|Hard| O(n^2)| O(n^2)|❤️|48.2%| |0039|Combination Sum|[Go]({{< relref "/ChapterFour/0001~0099/0039.Combination-Sum.md" >}})|Medium| O(n log n)| O(n)||60.6%| |0040|Combination Sum II|[Go]({{< relref "/ChapterFour/0001~0099/0040.Combination-Sum-II.md" >}})|Medium| O(n log n)| O(n)||50.9%| |0046|Permutations|[Go]({{< relref "/ChapterFour/0001~0099/0046.Permutations.md" >}})|Medium| O(n)| O(n)|❤️|68.0%| |0047|Permutations II|[Go]({{< relref "/ChapterFour/0001~0099/0047.Permutations-II.md" >}})|Medium| O(n^2)| O(n)|❤️|50.5%| |0051|N-Queens|[Go]({{< relref "/ChapterFour/0001~0099/0051.N-Queens.md" >}})|Hard| O(n!)| O(n)|❤️|52.3%| |0052|N-Queens II|[Go]({{< relref "/ChapterFour/0001~0099/0052.N-Queens-II.md" >}})|Hard| O(n!)| O(n)|❤️|62.7%| |0060|Permutation Sequence|[Go]({{< relref "/ChapterFour/0001~0099/0060.Permutation-Sequence.md" >}})|Hard| O(n log n)| O(1)||40.0%| |0077|Combinations|[Go]({{< relref "/ChapterFour/0001~0099/0077.Combinations.md" >}})|Medium| O(n)| O(n)|❤️|58.9%| |0078|Subsets|[Go]({{< relref "/ChapterFour/0001~0099/0078.Subsets.md" >}})|Medium| O(n^2)| O(n)|❤️|66.6%| |0079|Word Search|[Go]({{< relref "/ChapterFour/0001~0099/0079.Word-Search.md" >}})|Medium| O(n^2)| O(n^2)|❤️|37.7%| |0089|Gray Code|[Go]({{< relref "/ChapterFour/0001~0099/0089.Gray-Code.md" >}})|Medium| O(n)| O(1)||51.2%| |0090|Subsets II|[Go]({{< relref "/ChapterFour/0001~0099/0090.Subsets-II.md" >}})|Medium| O(n^2)| O(n)|❤️|49.7%| |0093|Restore IP Addresses|[Go]({{< relref "/ChapterFour/0001~0099/0093.Restore-IP-Addresses.md" >}})|Medium| O(n)| O(n)|❤️|38.5%| |0126|Word Ladder II|[Go]({{< relref "/ChapterFour/0100~0199/0126.Word-Ladder-II.md" >}})|Hard| O(n)| O(n^2)|❤️|24.2%| |0131|Palindrome Partitioning|[Go]({{< relref "/ChapterFour/0100~0199/0131.Palindrome-Partitioning.md" >}})|Medium| O(n)| O(n^2)|❤️|53.7%| |0211|Design Add and Search Words Data Structure|[Go]({{< relref "/ChapterFour/0200~0299/0211.Design-Add-and-Search-Words-Data-Structure.md" >}})|Medium| O(n)| O(n)|❤️|41.3%| |0212|Word Search II|[Go]({{< relref "/ChapterFour/0200~0299/0212.Word-Search-II.md" >}})|Hard| O(n^2)| O(n^2)|❤️|37.8%| |0216|Combination Sum III|[Go]({{< relref "/ChapterFour/0200~0299/0216.Combination-Sum-III.md" >}})|Medium| O(n)| O(1)|❤️|61.3%| |0306|Additive Number|[Go]({{< relref "/ChapterFour/0300~0399/0306.Additive-Number.md" >}})|Medium| O(n^2)| O(1)|❤️|29.9%| |0357|Count Numbers with Unique Digits|[Go]({{< relref "/ChapterFour/0300~0399/0357.Count-Numbers-with-Unique-Digits.md" >}})|Medium| O(1)| O(1)||49.3%| |0401|Binary Watch|[Go]({{< relref "/ChapterFour/0400~0499/0401.Binary-Watch.md" >}})|Easy| O(1)| O(1)||48.9%| |0526|Beautiful Arrangement|[Go]({{< relref "/ChapterFour/0500~0599/0526.Beautiful-Arrangement.md" >}})|Medium| O(n^2)| O(1)|❤️|62.4%| |0784|Letter Case Permutation|[Go]({{< relref "/ChapterFour/0700~0799/0784.Letter-Case-Permutation.md" >}})|Medium| O(n)| O(n)||69.2%| |0842|Split Array into Fibonacci Sequence|[Go]({{< relref "/ChapterFour/0800~0899/0842.Split-Array-into-Fibonacci-Sequence.md" >}})|Medium| O(n^2)| O(1)|❤️|37.1%| |0980|Unique Paths III|[Go]({{< relref "/ChapterFour/0900~0999/0980.Unique-Paths-III.md" >}})|Hard| O(n log n)| O(n)||77.1%| |0996|Number of Squareful Arrays|[Go]({{< relref "/ChapterFour/0900~0999/0996.Number-of-Squareful-Arrays.md" >}})|Hard| O(n log n)| O(n) ||48.6%| |1079|Letter Tile Possibilities|[Go]({{< relref "/ChapterFour/1000~1099/1079.Letter-Tile-Possibilities.md" >}})|Medium| O(n^2)| O(1)|❤️|76.1%| |1239|Maximum Length of a Concatenated String with Unique Characters|[Go]({{< relref "/ChapterFour/1200~1299/1239.Maximum-Length-of-a-Concatenated-String-with-Unique-Characters.md" >}})|Medium||||50.5%| |1641|Count Sorted Vowel Strings|[Go]({{< relref "/ChapterFour/1600~1699/1641.Count-Sorted-Vowel-Strings.md" >}})|Medium||||75.0%| |1655|Distribute Repeating Integers|[Go]({{< relref "/ChapterFour/1600~1699/1655.Distribute-Repeating-Integers.md" >}})|Hard||||40.2%| |1659|Maximize Grid Happiness|[Go]({{< relref "/ChapterFour/1600~1699/1659.Maximize-Grid-Happiness.md" >}})|Hard||||35.9%| |1681|Minimum Incompatibility|[Go]({{< relref "/ChapterFour/1600~1699/1681.Minimum-Incompatibility.md" >}})|Hard||||35.9%| |1688|Count of Matches in Tournament|[Go]({{< relref "/ChapterFour/1600~1699/1688.Count-of-Matches-in-Tournament.md" >}})|Easy||||81.8%| 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