From e0d71863c590e37f61c7c135fa5e3a99de8fc0a0 Mon Sep 17 00:00:00 2001 From: Ryhsman Date: Mon, 6 Sep 2021 23:02:35 +0800 Subject: [PATCH 01/10] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=E8=8A=82=E7=82=B9?= =?UTF-8?q?=E5=86=85=E5=AD=98=E9=87=8A=E6=94=BE=E4=BB=A3=E7=A0=81?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- .../0450.删除二叉搜索树中的节点.md | 22 +++++++++++++++++-- 1 file changed, 20 insertions(+), 2 deletions(-) diff --git a/problems/0450.删除二叉搜索树中的节点.md b/problems/0450.删除二叉搜索树中的节点.md index 35c8e24d..aa6bee76 100644 --- a/problems/0450.删除二叉搜索树中的节点.md +++ b/problems/0450.删除二叉搜索树中的节点.md @@ -118,10 +118,28 @@ public: if (root == nullptr) return root; // 第一种情况：没找到删除的节点，遍历到空节点直接返回了 if (root->val == key) { // 第二种情况：左右孩子都为空（叶子节点），直接删除节点， 返回NULL为根节点 + if (root->left == nullptr && root->right == nullptr) + { + ///! 内存释放 + delete root; + return nullptr; + } // 第三种情况：其左孩子为空，右孩子不为空，删除节点，右孩子补位 ，返回右孩子为根节点 - if (root->left == nullptr) return root->right; + else if (root->left == nullptr) + { + auto retNode = root->right; + ///! 内存释放 + delete root; + return retNode; + } // 第四种情况：其右孩子为空，左孩子不为空，删除节点，左孩子补位，返回左孩子为根节点 - else if (root->right == nullptr) return root->left; + else if (root->right == nullptr) + { + auto retNode = root->left; + ///! 内存释放 + delete root; + return retNode; + } // 第五种情况：左右孩子节点都不为空，则将删除节点的左子树放到删除节点的右子树的最左面节点的左孩子的位置 // 并返回删除节点右孩子为新的根节点。 else { From 0fa9cc1b070acfd76945e7593c07e7c87e23f641 Mon Sep 17 00:00:00 2001 From: Ryhsman Date: Mon, 6 Sep 2021 23:14:02 +0800 Subject: [PATCH 02/10] =?UTF-8?q?=E8=B0=83=E6=95=B4=E6=B7=BB=E5=8A=A0?= =?UTF-8?q?=E7=9A=84c++=E4=BB=A3=E7=A0=81=E6=A0=BC=E5=BC=8F=EF=BC=8C?= =?UTF-8?q?=E4=B8=8E=E6=95=B4=E4=BD=93=E7=BB=9F=E4=B8=80?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- problems/0450.删除二叉搜索树中的节点.md | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-) diff --git a/problems/0450.删除二叉搜索树中的节点.md b/problems/0450.删除二叉搜索树中的节点.md index aa6bee76..b8a1ae87 100644 --- a/problems/0450.删除二叉搜索树中的节点.md +++ b/problems/0450.删除二叉搜索树中的节点.md @@ -118,23 +118,20 @@ public: if (root == nullptr) return root; // 第一种情况：没找到删除的节点，遍历到空节点直接返回了 if (root->val == key) { // 第二种情况：左右孩子都为空（叶子节点），直接删除节点， 返回NULL为根节点 - if (root->left == nullptr && root->right == nullptr) - { + if (root->left == nullptr && root->right == nullptr) { ///! 内存释放 delete root; return nullptr; } // 第三种情况：其左孩子为空，右孩子不为空，删除节点，右孩子补位 ，返回右孩子为根节点 - else if (root->left == nullptr) - { + else if (root->left == nullptr) { auto retNode = root->right; ///! 内存释放 delete root; return retNode; } // 第四种情况：其右孩子为空，左孩子不为空，删除节点，左孩子补位，返回左孩子为根节点 - else if (root->right == nullptr) - { + else if (root->right == nullptr) { auto retNode = root->left; ///! 内存释放 delete root; From 5769c6c7e3af60c6bd4dcaa6441caa1c709303e7 Mon Sep 17 00:00:00 2001 From: ironartisan <54694467+ironartisan@users.noreply.github.com> Date: Tue, 7 Sep 2021 10:26:57 +0800 Subject: [PATCH 03/10] =?UTF-8?q?=E6=B7=BB=E5=8A=A00530.=E4=BA=8C=E5=8F=89?= =?UTF-8?q?=E6=90=9C=E7=B4=A2=E6=A0=91=E7=9A=84=E6=9C=80=E5=B0=8F=E7=BB=9D?= =?UTF-8?q?=E5=AF=B9=E5=80=BC=E5=B7=AE.md=E8=BF=AD=E4=BB=A3Java=E8=A7=A3?= =?UTF-8?q?=E6=B3=95?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- .../0530.二叉搜索树的最小绝对差.md | 27 +++++++++++++++++++ 1 file changed, 27 insertions(+) diff --git a/problems/0530.二叉搜索树的最小绝对差.md b/problems/0530.二叉搜索树的最小绝对差.md index ae6719ec..db2ca2d4 100644 --- a/problems/0530.二叉搜索树的最小绝对差.md +++ b/problems/0530.二叉搜索树的最小绝对差.md @@ -171,7 +171,34 @@ class Solution { } } ``` +迭代法-中序遍历 +```java +class Solution { + TreeNode pre; + Stack stack; + public int getMinimumDifference(TreeNode root) { + if (root == null) return 0; + stack = new Stack<>(); + TreeNode cur = root; + int result = Integer.MAX_VALUE; + while (cur != null || !stack.isEmpty()) { + if (cur != null) { + stack.push(cur); + cur = cur.left; // 左节点入栈 + }else { + cur = stack.pop(); // 右节点入栈 + if (pre != null) { + result = Math.min(result, cur.val - pre.val); + } + pre = cur; + cur = cur.right; + } + } + return result; + } +} +``` ## Python 递归 From 300f4a32d115c6b28ccbbbf664acf2a2471b65a1 Mon Sep 17 00:00:00 2001 From: ironartisan <54694467+ironartisan@users.noreply.github.com> Date: Tue, 7 Sep 2021 10:29:23 +0800 Subject: [PATCH 04/10] =?UTF-8?q?=E6=9B=B4=E6=96=B00530.=E4=BA=8C=E5=8F=89?= =?UTF-8?q?=E6=90=9C=E7=B4=A2=E6=A0=91=E7=9A=84=E6=9C=80=E5=B0=8F=E7=BB=9D?= =?UTF-8?q?=E5=AF=B9=E5=80=BC=E5=B7=AE.md=E8=BF=AD=E4=BB=A3Java=E6=B3=A8?= =?UTF-8?q?=E9=87=8A?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- problems/0530.二叉搜索树的最小绝对差.md | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/problems/0530.二叉搜索树的最小绝对差.md b/problems/0530.二叉搜索树的最小绝对差.md index db2ca2d4..b19a0dd2 100644 --- a/problems/0530.二叉搜索树的最小绝对差.md +++ b/problems/0530.二叉搜索树的最小绝对差.md @@ -184,15 +184,15 @@ class Solution { int result = Integer.MAX_VALUE; while (cur != null || !stack.isEmpty()) { if (cur != null) { - stack.push(cur); - cur = cur.left; // 左节点入栈 + stack.push(cur); // 将访问的节点放进栈 + cur = cur.left; // 左 }else { - cur = stack.pop(); // 右节点入栈 - if (pre != null) { + cur = stack.pop(); + if (pre != null) { // 中 result = Math.min(result, cur.val - pre.val); } pre = cur; - cur = cur.right; + cur = cur.right; // 右 } } return result; From 92980de383398d6540a48dcf648996df00726408 Mon Sep 17 00:00:00 2001 From: ironartisan <54694467+ironartisan@users.noreply.github.com> Date: Tue, 7 Sep 2021 11:28:50 +0800 Subject: [PATCH 05/10] =?UTF-8?q?=E6=B7=BB=E5=8A=A00501.=E4=BA=8C=E5=8F=89?= =?UTF-8?q?=E6=90=9C=E7=B4=A2=E6=A0=91=E4=B8=AD=E7=9A=84=E4=BC=97=E6=95=B0?= =?UTF-8?q?.md=E8=BF=AD=E4=BB=A3Java=E8=A7=A3=E6=B3=95?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- problems/0501.二叉搜索树中的众数.md | 38 ++++++++++++++++++++ 1 file changed, 38 insertions(+) diff --git a/problems/0501.二叉搜索树中的众数.md b/problems/0501.二叉搜索树中的众数.md index aeddc600..22d4f4ac 100644 --- a/problems/0501.二叉搜索树中的众数.md +++ b/problems/0501.二叉搜索树中的众数.md @@ -429,6 +429,44 @@ class Solution { } } ``` +迭代法 +```java +class Solution { + public int[] findMode(TreeNode root) { + TreeNode pre = null; + Stack stack = new Stack<>(); + List result = new ArrayList<>(); + int maxCount = 0; + int count = 0; + TreeNode cur = root; + while (cur != null || !stack.isEmpty()) { + if (cur != null) { + stack.push(cur); + cur =cur.left; + }else { + cur = stack.pop(); + // 计数 + if (pre == null || cur.val != pre.val) { + count = 1; + }else { + count++; + } + // 更新结果 + if (count > maxCount) { + maxCount = count; + result.clear(); + result.add(cur.val); + }else if (count == maxCount) { + result.add(cur.val); + } + pre = cur; + cur = cur.right; + } + } + return result.stream().mapToInt(Integer::intValue).toArray(); + } +} +``` ## Python From b5b7437a5516382eb3410184a26fa33045814548 Mon Sep 17 00:00:00 2001 From: ironartisan <54694467+ironartisan@users.noreply.github.com> Date: Tue, 7 Sep 2021 14:04:28 +0800 Subject: [PATCH 06/10] =?UTF-8?q?=E6=B7=BB=E5=8A=A00235.=E4=BA=8C=E5=8F=89?= =?UTF-8?q?=E6=90=9C=E7=B4=A2=E6=A0=91=E7=9A=84=E6=9C=80=E8=BF=91=E5=85=AC?= =?UTF-8?q?=E5=85=B1=E7=A5=96=E5=85=88.md=E9=80=92=E5=BD=92Java=E8=A7=A3?= =?UTF-8?q?=E6=B3=95?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- problems/0235.二叉搜索树的最近公共祖先.md | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/problems/0235.二叉搜索树的最近公共祖先.md b/problems/0235.二叉搜索树的最近公共祖先.md index 929e6eb2..25bbf7e4 100644 --- a/problems/0235.二叉搜索树的最近公共祖先.md +++ b/problems/0235.二叉搜索树的最近公共祖先.md @@ -234,7 +234,15 @@ public: ## Java 递归法： - +```java +class Solution { + public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) { + if (root.val > p.val && root.val > q.val) return lowestCommonAncestor(root.left, p, q); + if (root.val < p.val && root.val < q.val) return lowestCommonAncestor(root.right, p, q); + return root; + } +} +``` 迭代法： ```java From 4d91c78e1ea6e1d51a5a73b825762cf6097a1e96 Mon Sep 17 00:00:00 2001 From: Asterisk <44215173+GHumorBS@users.noreply.github.com> Date: Tue, 7 Sep 2021 17:00:25 +0800 Subject: [PATCH 07/10] =?UTF-8?q?Update=200406.=E6=A0=B9=E6=8D=AE=E8=BA=AB?= =?UTF-8?q?=E9=AB=98=E9=87=8D=E5=BB=BA=E9=98=9F=E5=88=97.md?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 补充一下python注释，更好理解python语法 --- problems/0406.根据身高重建队列.md | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/problems/0406.根据身高重建队列.md b/problems/0406.根据身高重建队列.md index 6d8f703b..bd27b1b2 100644 --- a/problems/0406.根据身高重建队列.md +++ b/problems/0406.根据身高重建队列.md @@ -209,8 +209,13 @@ Python： ```python class Solution: def reconstructQueue(self, people: List[List[int]]) -> List[List[int]]: + # 先按照h维度的身高顺序从高到低排序。确定第一个维度 + # lambda返回的是一个元组：当-x[0](维度h）相同时，再根据x[1]（维度k）从小到大排序 people.sort(key=lambda x: (-x[0], x[1])) que = [] + + # 根据每个元素的第二个维度k，贪心算法，进行插入 + # people已经排序过了：同一高度时k值小的排前面。 for p in people: que.insert(p[1], p) return que From d52cb2aa4901be727d077c2aaf3aafd9ed0519ee Mon Sep 17 00:00:00 2001 From: ironartisan <54694467+ironartisan@users.noreply.github.com> Date: Tue, 7 Sep 2021 21:47:41 +0800 Subject: [PATCH 08/10] =?UTF-8?q?=E6=B7=BB=E5=8A=A00450.=E5=88=A0=E9=99=A4?= =?UTF-8?q?=E4=BA=8C=E5=8F=89=E6=90=9C=E7=B4=A2=E6=A0=91=E4=B8=AD=E7=9A=84?= =?UTF-8?q?=E8=8A=82=E7=82=B9.mdJava=E8=A7=A3=E6=B3=95?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- .../0450.删除二叉搜索树中的节点.md | 27 +++++++++++++++++++ 1 file changed, 27 insertions(+) diff --git a/problems/0450.删除二叉搜索树中的节点.md b/problems/0450.删除二叉搜索树中的节点.md index 35c8e24d..6b8ab7ed 100644 --- a/problems/0450.删除二叉搜索树中的节点.md +++ b/problems/0450.删除二叉搜索树中的节点.md @@ -278,6 +278,33 @@ class Solution { } } ``` +```java +// 解法2 +class Solution { + public TreeNode deleteNode(TreeNode root, int key) { + if (root == null) return root; + if (root.val == key) { + if (root.left == null) { + return root.right; + } + else if (root.right == null) { + return root.left; + } + else{ + TreeNode cur = root.right; + while (cur.left != null) { + cur = cur.left; + } + cur.left = root.left; + root = root.right; + return root; + } + } + if (root.val > key) root.left = deleteNode(root.left, key); + if (root.val < key) root.right = deleteNode(root.right, key); + return root; + } +``` ## Python From 6a6d6f993aa496788325d1f4bb0d95c44ede202b Mon Sep 17 00:00:00 2001 From: ironartisan <54694467+ironartisan@users.noreply.github.com> Date: Tue, 7 Sep 2021 21:48:13 +0800 Subject: [PATCH 09/10] =?UTF-8?q?=E6=B7=BB=E5=8A=A00450.=E5=88=A0=E9=99=A4?= =?UTF-8?q?=E4=BA=8C=E5=8F=89=E6=90=9C=E7=B4=A2=E6=A0=91=E4=B8=AD=E7=9A=84?= =?UTF-8?q?=E8=8A=82=E7=82=B9.mdJava=E8=A7=A3=E6=B3=95?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- .../0450.删除二叉搜索树中的节点.md | 39 +++++++++---------- 1 file changed, 19 insertions(+), 20 deletions(-) diff --git a/problems/0450.删除二叉搜索树中的节点.md b/problems/0450.删除二叉搜索树中的节点.md index 6b8ab7ed..f11431e0 100644 --- a/problems/0450.删除二叉搜索树中的节点.md +++ b/problems/0450.删除二叉搜索树中的节点.md @@ -281,29 +281,28 @@ class Solution { ```java // 解法2 class Solution { - public TreeNode deleteNode(TreeNode root, int key) { - if (root == null) return root; - if (root.val == key) { - if (root.left == null) { - return root.right; - } - else if (root.right == null) { - return root.left; - } - else{ - TreeNode cur = root.right; - while (cur.left != null) { - cur = cur.left; - } - cur.left = root.left; - root = root.right; - return root; - } + public TreeNode deleteNode(TreeNode root, int key) { + if (root == null) return root; + if (root.val == key) { + if (root.left == null) { + return root.right; + } else if (root.right == null) { + return root.left; + } else { + TreeNode cur = root.right; + while (cur.left != null) { + cur = cur.left; } - if (root.val > key) root.left = deleteNode(root.left, key); - if (root.val < key) root.right = deleteNode(root.right, key); + cur.left = root.left; + root = root.right; return root; + } } + if (root.val > key) root.left = deleteNode(root.left, key); + if (root.val < key) root.right = deleteNode(root.right, key); + return root; + } +} ``` ## Python From 995aa86ab2eb21559bcdd0d3cc91e486e33cade1 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?=E6=9E=81=E5=AE=A2=E5=AD=A6=E4=BC=9F?= Date: Wed, 8 Sep 2021 13:28:04 +0800 Subject: [PATCH 10/10] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=20=E7=AC=AC18=E9=A2=98?= =?UTF-8?q?.=20=E5=9B=9B=E6=95=B0=E4=B9=8B=E5=92=8C=20Swift=E7=89=88?= =?UTF-8?q?=E6=9C=AC?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- problems/0018.四数之和.md | 48 +++++++++++++++++++++++++++++++++++ 1 file changed, 48 insertions(+) diff --git a/problems/0018.四数之和.md b/problems/0018.四数之和.md index c81c5df7..9891f0fe 100644 --- a/problems/0018.四数之和.md +++ b/problems/0018.四数之和.md @@ -354,6 +354,54 @@ class Solution { } ``` +Swift: +```swift +func fourSum(_ nums: [Int], _ target: Int) -> [[Int]] { + var res = [[Int]]() + var sorted = nums + sorted.sort() + for k in 0 ..< sorted.count { + // 这种剪枝不行,target可能是负数 +// if sorted[k] > target { +// return res +// } + // 去重 + if k > 0 && sorted[k] == sorted[k - 1] { + continue + } + + let target2 = target - sorted[k] + for i in (k + 1) ..< sorted.count { + if i > (k + 1) && sorted[i] == sorted[i - 1] { + continue + } + var left = i + 1 + var right = sorted.count - 1 + while left < right { + let sum = sorted[i] + sorted[left] + sorted[right] + if sum < target2 { + left += 1 + } else if sum > target2 { + right -= 1 + } else { + res.append([sorted[k], sorted[i], sorted[left], sorted[right]]) + while left < right && sorted[left] == sorted[left + 1] { + left += 1 + } + while left < right && sorted[right] == sorted[right - 1] { + right -= 1 + } + // 找到答案 双指针同时收缩 + left += 1 + right -= 1 + } + } + } + } + return res +} +``` + ----------------------- * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw) * B站视频：[代码随想录](https://space.bilibili.com/525438321)