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‎Problemset/0212-Word Search II/README.md

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# 212. Word Search II
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Given an `m x n` `board` of characters and a list of strings `words`, return *all words on the board*.
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Each word must be constructed from letters of sequentially adjacent cells, where **adjacent cells** are horizontally or vertically neighboring. The same letter cell may not be used more than once in a word.
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#### Example 1:
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![](https://assets.leetcode.com/uploads/2020/11/07/search1.jpg)
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<pre>
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<strong>Input:</strong> board = [["o","a","a","n"],["e","t","a","e"],["i","h","k","r"],["i","f","l","v"]], words = ["oath","pea","eat","rain"]
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<strong>Output:</strong> ["eat","oath"]
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</pre>
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#### Example 2:
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![](https://assets.leetcode.com/uploads/2020/11/07/search2.jpg)
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<pre>
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<strong>Input:</strong> board = [["a","b"],["c","d"]], words = ["abcb"]
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<strong>Output:</strong> []
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</pre>
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#### Constraints:
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* `m == board.length`
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* `n == board[i].length`
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* `1 <= m, n <= 12`
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* `board[i][j]` is a lowercase English letter.
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* <code>1 <= words.length <= 3 * 10<sup>4</sup></code>
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* `1 <= words[i].length <= 10`
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* `words[i]` consists of lowercase English letters.
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* All the strings of `words` are unique.
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## Solutions (Python)
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### 1. Solution
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```Python
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class Solution:
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def findWords(self, board: List[List[str]], words: List[str]) -> List[str]:
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def dfs(i: int, j: int, root: dict) -> None:
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if (i, j) in visited or i < 0 or i >= m or j < 0 or j >= n or board[i][j] not in root:
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return None
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if root[board[i][j]][0] != "":
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ret.append(root[board[i][j]][0])
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root[board[i][j]][0] = ""
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visited.add((i, j))
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dfs(i - 1, j, root[board[i][j]][1])
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dfs(i + 1, j, root[board[i][j]][1])
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dfs(i, j - 1, root[board[i][j]][1])
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dfs(i, j + 1, root[board[i][j]][1])
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visited.remove((i, j))
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m, n = len(board), len(board[0])
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root = {}
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visited = set()
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ret = []
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for word in words:
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curr = root
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for i, c in enumerate(word):
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if c not in curr:
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curr[c] = ["", {}]
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if i == len(word) - 1:
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curr[c][0] = word
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curr = curr[c][1]
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for i in range(m):
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for j in range(n):
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dfs(i, j, root)
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return ret
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```

‎Problemset/0212-Word Search II/README_CN.md

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# 212. 单词搜索 II
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给定一个 `m x n` 二维字符网格 `board` 和一个单词（字符串）列表 `words`， *返回所有二维网格上的单词* 。
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单词必须按照字母顺序，通过 **相邻的单元格** 内的字母构成，其中“相邻”单元格是那些水平相邻或垂直相邻的单元格。同一个单元格内的字母在一个单词中不允许被重复使用。
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#### 示例 1:
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![](https://assets.leetcode.com/uploads/2020/11/07/search1.jpg)
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<pre>
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<strong>输入:</strong> board = [["o","a","a","n"],["e","t","a","e"],["i","h","k","r"],["i","f","l","v"]], words = ["oath","pea","eat","rain"]
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<strong>输出:</strong> ["eat","oath"]
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</pre>
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#### 示例 2:
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![](https://assets.leetcode.com/uploads/2020/11/07/search2.jpg)
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<pre>
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<strong>输入:</strong> board = [["a","b"],["c","d"]], words = ["abcb"]
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<strong>输出:</strong> []
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</pre>
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#### 提示:
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* `m == board.length`
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* `n == board[i].length`
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* `1 <= m, n <= 12`
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* `board[i][j]` 是一个小写英文字母
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* <code>1 <= words.length <= 3 * 10<sup>4</sup></code>
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* `1 <= words[i].length <= 10`
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* `words[i]` 由小写英文字母组成
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* `words` 中的所有字符串互不相同
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## 题解 (Python)
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### 1. 题解
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```Python
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class Solution:
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def findWords(self, board: List[List[str]], words: List[str]) -> List[str]:
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def dfs(i: int, j: int, root: dict) -> None:
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if (i, j) in visited or i < 0 or i >= m or j < 0 or j >= n or board[i][j] not in root:
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return None
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if root[board[i][j]][0] != "":
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ret.append(root[board[i][j]][0])
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root[board[i][j]][0] = ""
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visited.add((i, j))
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dfs(i - 1, j, root[board[i][j]][1])
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dfs(i + 1, j, root[board[i][j]][1])
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dfs(i, j - 1, root[board[i][j]][1])
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dfs(i, j + 1, root[board[i][j]][1])
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visited.remove((i, j))
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m, n = len(board), len(board[0])
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root = {}
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visited = set()
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ret = []
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for word in words:
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curr = root
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for i, c in enumerate(word):
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if c not in curr:
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curr[c] = ["", {}]
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if i == len(word) - 1:
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curr[c][0] = word
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curr = curr[c][1]
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for i in range(m):
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for j in range(n):
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dfs(i, j, root)
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return ret
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```

‎Problemset/0212-Word Search II/Solution.py

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class Solution:
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def findWords(self, board: List[List[str]], words: List[str]) -> List[str]:
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def dfs(i: int, j: int, root: dict) -> None:
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if (i, j) in visited or i < 0 or i >= m or j < 0 or j >= n or board[i][j] not in root:
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return None
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if root[board[i][j]][0] != "":
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ret.append(root[board[i][j]][0])
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root[board[i][j]][0] = ""
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visited.add((i, j))
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dfs(i - 1, j, root[board[i][j]][1])
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dfs(i + 1, j, root[board[i][j]][1])
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dfs(i, j - 1, root[board[i][j]][1])
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dfs(i, j + 1, root[board[i][j]][1])
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visited.remove((i, j))
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m, n = len(board), len(board[0])
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root = {}
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visited = set()
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ret = []
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for word in words:
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curr = root
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for i, c in enumerate(word):
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if c not in curr:
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curr[c] = ["", {}]
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if i == len(word) - 1:
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curr[c][0] = word
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curr = curr[c][1]
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for i in range(m):
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for j in range(n):
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dfs(i, j, root)
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return ret

‎README.md

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[209][209l] |[Minimum Size Subarray Sum][209] |![rs]
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[210][210l] |[Course Schedule II][210] |![rs]
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[211][211l] |[Design Add and Search Words Data Structure][211] |![py]
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[212][212l] |[Word Search II][212] |![py]
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[213][213l] |[House Robber II][213] |![rs]
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[215][215l] |[Kth Largest Element in an Array][215] |![rb]
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[216][216l] |[Combination Sum III][216] |![rs]
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[209]:Problemset/0209-Minimum%20Size%20Subarray%20Sum/README.md#209-minimum-size-subarray-sum
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[210]:Problemset/0210-Course%20Schedule%20II/README.md#210-course-schedule-ii
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[211]:Problemset/0211-Design%20Add%20and%20Search%20Words%20Data%20Structure/README.md#211-design-add-and-search-words-data-structure
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[212]:Problemset/0212-Word%20Search%20II/README.md#212-word-search-ii
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[213]:Problemset/0213-House%20Robber%20II/README.md#213-house-robber-ii
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[215]:Problemset/0215-Kth%20Largest%20Element%20in%20an%20Array/README.md#215-kth-largest-element-in-an-array
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[216]:Problemset/0216-Combination%20Sum%20III/README.md#216-combination-sum-iii
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[209l]:https://leetcode.com/problems/minimum-size-subarray-sum/
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[210l]:https://leetcode.com/problems/course-schedule-ii/
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[211l]:https://leetcode.com/problems/add-and-search-word-data-structure-design/
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[212l]:https://leetcode.com/problems/word-search-ii/
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[213l]:https://leetcode.com/problems/house-robber-ii/
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[215l]:https://leetcode.com/problems/kth-largest-element-in-an-array/
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[216l]:https://leetcode.com/problems/combination-sum-iii/

‎README_CN.md

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[209][209l] |[长度最小的子数组][209] |![rs]
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[210][210l] |[课程表 II][210] |![rs]
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[211][211l] |[添加与搜索单词 - 数据结构设计][211] |![py]
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[212][212l] |[单词搜索 II][212] |![py]
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[213][213l] |[打家劫舍 II][213] |![rs]
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[215][215l] |[数组中的第K个最大元素][215] |![rb]
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[216][216l] |[组合总和 III][216] |![rs]
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[209]:Problemset/0209-Minimum%20Size%20Subarray%20Sum/README_CN.md#209-长度最小的子数组
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[210]:Problemset/0210-Course%20Schedule%20II/README_CN.md#210-课程表-ii
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[211]:Problemset/0211-Design%20Add%20and%20Search%20Words%20Data%20Structure/README_CN.md#211-添加与搜索单词---数据结构设计
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[212]:Problemset/0212-Word%20Search%20II/README_CN.md#212-单词搜索-ii
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[213]:Problemset/0213-House%20Robber%20II/README_CN.md#213-打家劫舍-ii
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[215]:Problemset/0215-Kth%20Largest%20Element%20in%20an%20Array/README_CN.md#215-数组中的第k个最大元素
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[216]:Problemset/0216-Combination%20Sum%20III/README_CN.md#216-组合总和-iii
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[209l]:https://leetcode.cn/problems/minimum-size-subarray-sum/
35293531
[210l]:https://leetcode.cn/problems/course-schedule-ii/
35303532
[211l]:https://leetcode.cn/problems/add-and-search-word-data-structure-design/
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[212l]:https://leetcode.cn/problems/word-search-ii/
35313534
[213l]:https://leetcode.cn/problems/house-robber-ii/
35323535
[215l]:https://leetcode.cn/problems/kth-largest-element-in-an-array/
35333536
[216l]:https://leetcode.cn/problems/combination-sum-iii/

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