diff --git a/problems/0015.三数之和.md b/problems/0015.三数之和.md index dec8a7c6..1e675254 100644 --- a/problems/0015.三数之和.md +++ b/problems/0015.三数之和.md @@ -435,5 +435,79 @@ func threeSum(_ nums: [Int]) -> [[Int]] { } ``` +C: +```C +//qsort辅助cmp函数 +int cmp(const void* ptr1, const void* ptr2) { + return *((int*)ptr1) > *((int*)ptr2); +} + +int** threeSum(int* nums, int numsSize, int* returnSize, int** returnColumnSizes) { + //开辟ans数组空间 + int **ans = (int**)malloc(sizeof(int*) * 18000); + int ansTop = 0; + //若传入nums数组大小小于3,则需要返回数组大小为0 + if(numsSize < 3) { + *returnSize = 0; + return ans; + } + //对nums数组进行排序 + qsort(nums, numsSize, sizeof(int), cmp); + + + int i; + //用for循环遍历数组,结束条件为i < numsSize - 2(因为要预留左右指针的位置) + for(i = 0; i < numsSize - 2; i++) { + //若当前i指向元素>0,则代表left和right以及i的和大于0。直接break + if(nums[i] > 0) + break; + //去重:i > 0 && nums[i] == nums[i-1] + if(i > 0 && nums[i] == nums[i-1]) + continue; + //定义左指针和右指针 + int left = i + 1; + int right = numsSize - 1; + //当右指针比左指针大时进行循环 + while(right > left) { + //求出三数之和 + int sum = nums[right] + nums[left] + nums[i]; + //若和小于0,则左指针+1(因为左指针右边的数比当前所指元素大) + if(sum < 0) + left++; + //若和大于0,则将右指针-1 + else if(sum > 0) + right--; + //若和等于0 + else { + //开辟一个大小为3的数组空间,存入nums[i], nums[left]和nums[right] + int* arr = (int*)malloc(sizeof(int) * 3); + arr[0] = nums[i]; + arr[1] = nums[left]; + arr[2] = nums[right]; + //将开辟数组存入ans中 + ans[ansTop++] = arr; + //去重 + while(right > left && nums[right] == nums[right - 1]) + right--; + while(left < right && nums[left] == nums[left + 1]) + left++; + //更新左右指针 + left++; + right--; + } + } + } + + //设定返回的数组大小 + *returnSize = ansTop; + *returnColumnSizes = (int*)malloc(sizeof(int) * ansTop); + int z; + for(z = 0; z < ansTop; z++) { + (*returnColumnSizes)[z] = 3; + } + return ans; +} +``` + -----------------------
diff --git a/problems/0019.删除链表的倒数第N个节点.md b/problems/0019.删除链表的倒数第N个节点.md index e05b9d03..188c4c57 100644 --- a/problems/0019.删除链表的倒数第N个节点.md +++ b/problems/0019.删除链表的倒数第N个节点.md @@ -173,8 +173,7 @@ var removeNthFromEnd = function(head, n) { let ret = new ListNode(0, head), slow = fast = ret; while(n--) fast = fast.next; - if(!fast) return ret.next; - while (fast.next) { + while (fast.next !== null) { fast = fast.next; slow = slow.next }; diff --git a/problems/0040.组合总和II.md b/problems/0040.组合总和II.md index bab4bd6a..b5e511e7 100644 --- a/problems/0040.组合总和II.md +++ b/problems/0040.组合总和II.md @@ -457,6 +457,37 @@ var combinationSum2 = function(candidates, target) { } }; ``` +**使用used去重** +```js +var combinationSum2 = function(candidates, target) { + let res = []; + let path = []; + let total = 0; + const len = candidates.length; + candidates.sort((a, b) => a - b); + let used = new Array(len).fill(false); + const backtracking = (startIndex) => { + if (total === target) { + res.push([...path]); + return; + } + for(let i = startIndex; i < len && total < target; i++) { + const cur = candidates[i]; + if (cur > target - total || (i > 0 && cur === candidates[i - 1] && !used[i - 1])) continue; + path.push(cur); + total += cur; + used[i] = true; + backtracking(i + 1); + path.pop(); + total -= cur; + used[i] = false; + } + } + backtracking(0); + return res; +}; +``` + ## C ```c diff --git a/problems/0098.验证二叉搜索树.md b/problems/0098.验证二叉搜索树.md index ec265615..82d1941e 100644 --- a/problems/0098.验证二叉搜索树.md +++ b/problems/0098.验证二叉搜索树.md @@ -414,19 +414,24 @@ class Solution: import "math" func isValidBST(root *TreeNode) bool { - if root == nil { - return true - } - return isBST(root, math.MinInt64, math.MaxFloat64) + // 二叉搜索树也可以是空树 + if root == nil { + return true + } + // 由题目中的数据限制可以得出min和max + return check(root,math.MinInt64,math.MaxInt64) } -func isBST(root *TreeNode, min, max int) bool { - if root == nil { - return true - } - if min >= root.Val || max <= root.Val { - return false - } - return isBST(root.Left, min, root.Val) && isBST(root.Right, root.Val, max) + +func check(node *TreeNode,min,max int64) bool { + if node == nil { + return true + } + + if min >= int64(node.Val) || max <= int64(node.Val) { + return false + } + // 分别对左子树和右子树递归判断,如果左子树和右子树都符合则返回true + return check(node.Right,int64(node.Val),max) && check(node.Left,min,int64(node.Val)) } ``` ```go diff --git a/problems/0150.逆波兰表达式求值.md b/problems/0150.逆波兰表达式求值.md index ef91330d..137aaf5d 100644 --- a/problems/0150.逆波兰表达式求值.md +++ b/problems/0150.逆波兰表达式求值.md @@ -241,6 +241,38 @@ class Solution: ``` +Swift: +```Swift +func evalRPN(_ tokens: [String]) -> Int { + var stack = [Int]() + for c in tokens { + let v = Int(c) + if let num = v { + // 遇到数字直接入栈 + stack.append(num) + } else { + // 遇到运算符, 取出栈顶两元素计算, 结果压栈 + var res: Int = 0 + let num2 = stack.popLast()! + let num1 = stack.popLast()! + switch c { + case "+": + res = num1 + num2 + case "-": + res = num1 - num2 + case "*": + res = num1 * num2 + case "/": + res = num1 / num2 + default: + break + } + stack.append(res) + } + } + return stack.last! +} +``` -----------------------
diff --git a/problems/0205.同构字符串.md b/problems/0205.同构字符串.md index a2963149..eeda7d2e 100644 --- a/problems/0205.同构字符串.md +++ b/problems/0205.同构字符串.md @@ -90,6 +90,24 @@ class Solution { ## Python ```python +class Solution: + def isIsomorphic(self, s: str, t: str) -> bool: + default_dict1 = defaultdict(str) + default_dict2 = defaultdict(str) + + if len(s) != len(t): return false + + for i in range(len(s)): + if not default_dict1[s[i]]: + default_dict1[s[i]] = t[i] + + if not default_dict2[t[i]]: + default_dict2[t[i]] = s[i] + + if default_dict1[s[i]] != t[i] or default_dict2[t[i]] != s[i]: + return False + + return True ``` ## Go diff --git a/problems/0236.二叉树的最近公共祖先.md b/problems/0236.二叉树的最近公共祖先.md index 4182999f..6d26e376 100644 --- a/problems/0236.二叉树的最近公共祖先.md +++ b/problems/0236.二叉树的最近公共祖先.md @@ -221,42 +221,30 @@ public: ## Java + ```Java class Solution { public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) { - return lowestCommonAncestor1(root, p, q); - } - public TreeNode lowestCommonAncestor1(TreeNode root, TreeNode p, TreeNode q) { - if (root == null || root == p || root == q) { + if (root == null || root == p || root == q) { // 递归结束条件 return root; } - TreeNode left = lowestCommonAncestor1(root.left, p, q); - TreeNode right = lowestCommonAncestor1(root.right, p, q); - if (left != null && right != null) {// 左右子树分别找到了,说明此时的root就是要求的结果 - return root; - } - if (left == null) { + + // 后序遍历 + TreeNode left = lowestCommonAncestor(root.left, p, q); + TreeNode right = lowestCommonAncestor(root.right, p, q); + + if(left == null && right == null) { // 若未找到节点 p 或 q + return null; + }else if(left == null && right != null) { // 若找到一个节点 return right; + }else if(left != null && right == null) { // 若找到一个节点 + return left; + }else { // 若找到两个节点 + return root; } - return left; } } -``` - -```java -// 代码精简版 -class Solution { - public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) { - if (root == null || root.val == p.val ||root.val == q.val) return root; - TreeNode left = lowestCommonAncestor(root.left,p,q); - TreeNode right = lowestCommonAncestor(root.right,p,q); - if (left != null && right != null) return root; - else if (left == null && right != null) return right; - else if (left != null && right == null) return left; - else return null; - } -} ``` ## Python diff --git a/problems/0239.滑动窗口最大值.md b/problems/0239.滑动窗口最大值.md index 8a8d3a52..1f245699 100644 --- a/problems/0239.滑动窗口最大值.md +++ b/problems/0239.滑动窗口最大值.md @@ -418,6 +418,112 @@ var maxSlidingWindow = function (nums, k) { }; ``` +Swift: +```Swift +/// 双向链表 +class DoublyListNode { + var head: DoublyListNode? + var tail: DoublyListNode? + var next: DoublyListNode? + var pre: DoublyListNode? + var value: Int = 0 + init(_ value: Int = 0) { + self.value = value + } + func isEmpty() -> Bool { + return self.head == nil + } + func first() -> Int? { + return self.head?.value + } + func last() -> Int? { + return self.tail?.value + } + func removeFirst() { + if isEmpty() { + return + } + let next = self.head!.next + self.head?.next = nil// 移除首节点 + next?.pre = nil + self.head = next + } + func removeLast() { + if let tail = self.tail { + if let pre = tail.pre { + self.tail?.pre = nil + pre.next = nil + self.tail = pre + } else { + self.head = nil + self.tail = nil + } + } + } + func append(_ value: Int) { + let node = DoublyListNode(value) + if self.head != nil { + node.pre = self.tail + self.tail?.next = node + self.tail = node + } else { + self.head = node + self.tail = node + self.pre = nil + self.next = nil + } + } +} +// 单调队列, 从大到小 +class MyQueue { +// var queue: [Int]!// 用数组会超时 + var queue: DoublyListNode! + init() { +// queue = [Int]() + queue = DoublyListNode() + } + // 滑动窗口时弹出第一个元素, 如果相等再弹出 + func pop(x: Int) { + if !queue.isEmpty() && front() == x { + queue.removeFirst() + } + } + // 滑动窗口时添加下一个元素, 移除队尾比 x 小的元素 始终保证队头 > 队尾 + func push(x: Int) { + while !queue.isEmpty() && queue.last()! < x { + queue.removeLast() + } + queue.append(x) + } + // 此时队头就是滑动窗口最大值 + func front() -> Int { + return queue.first() ?? -1 + } +} + +class Solution { + func maxSlidingWindow(_ nums: [Int], _ k: Int) -> [Int] { + // 存放结果 + var res = [Int]() + let queue = MyQueue() + // 先将前K个元素放入队列 + for i in 0 ..< k { + queue.push(x: nums[i]) + } + // 添加当前队列最大值到结果数组 + res.append(queue.front()) + for i in k ..< nums.count { + // 滑动窗口移除最前面元素 + queue.pop(x: nums[i - k]) + // 滑动窗口添加下一个元素 + queue.push(x: nums[i]) + // 保存当前队列最大值 + res.append(queue.front()) + } + return res + } +} +``` -----------------------
diff --git a/problems/0416.分割等和子集.md b/problems/0416.分割等和子集.md index b661a766..393baf7d 100644 --- a/problems/0416.分割等和子集.md +++ b/problems/0416.分割等和子集.md @@ -68,7 +68,7 @@ * 背包的体积为sum / 2 * 背包要放入的商品(集合里的元素)重量为 元素的数值,价值也为元素的数值 -* 背包如何正好装满,说明找到了总和为 sum / 2 的子集。 +* 背包如果正好装满,说明找到了总和为 sum / 2 的子集。 * 背包中每一个元素是不可重复放入。 以上分析完,我们就可以套用01背包,来解决这个问题了。 diff --git a/problems/0701.二叉搜索树中的插入操作.md b/problems/0701.二叉搜索树中的插入操作.md index 5d63ce58..1e6ab47e 100644 --- a/problems/0701.二叉搜索树中的插入操作.md +++ b/problems/0701.二叉搜索树中的插入操作.md @@ -236,16 +236,13 @@ class Solution { ```java class Solution { public TreeNode insertIntoBST(TreeNode root, int val) { - return buildTree(root, val); - } - - public TreeNode buildTree(TreeNode root, int val){ if (root == null) // 如果当前节点为空,也就意味着val找到了合适的位置,此时创建节点直接返回。 return new TreeNode(val); + if (root.val < val){ - root.right = buildTree(root.right, val); // 递归创建右子树 + root.right = insertIntoBST(root.right, val); // 递归创建右子树 }else if (root.val > val){ - root.left = buildTree(root.left, val); // 递归创建左子树 + root.left = insertIntoBST(root.left, val); // 递归创建左子树 } return root; } diff --git a/problems/0704.二分查找.md b/problems/0704.二分查找.md index bb10143f..44a0c1d8 100644 --- a/problems/0704.二分查找.md +++ b/problems/0704.二分查找.md @@ -276,11 +276,9 @@ func search(nums []int, target int) int { ``` **JavaScript:** +(版本一)左闭右闭区间 ```js - -// (版本一)左闭右闭区间 - /** * @param {number[]} nums * @param {number} target @@ -302,9 +300,10 @@ var search = function(nums, target) { } return -1; }; +``` +(版本二)左闭右开区间 -// (版本二)左闭右开区间 - +```js /** * @param {number[]} nums * @param {number} target @@ -325,7 +324,6 @@ var search = function(nums, target) { } return -1; }; - ``` **Ruby:** diff --git a/problems/0977.有序数组的平方.md b/problems/0977.有序数组的平方.md index b1e04c4e..6616ba8c 100644 --- a/problems/0977.有序数组的平方.md +++ b/problems/0977.有序数组的平方.md @@ -199,27 +199,26 @@ impl Solution { Javascript: ```Javascript /** - * @desc two pointers solution - * @link https://leetcode-cn.com/problems/squares-of-a-sorted-array/ - * @param nums Array e.g. [-4,-1,0,3,10] - * @return {array} e.g. [0,1,9,16,100] + * @param {number[]} nums + * @return {number[]} */ -const sortedSquares = function (nums) { - let res = [] - for (let i = 0, j = nums.length - 1; i <= j;) { - const left = Math.abs(nums[i]) - const right = Math.abs(nums[j]) - if (right > left) { - // push element to the front of the array - res.unshift(right * right) - j-- - } else { - res.unshift(left * left) - i++ - } +var sortedSquares = function(nums) { + let n = nums.length; + let res = new Array(n).fill(0); + let i = 0, j = n - 1, k = n - 1; + while (i <= j) { + let left = nums[i] * nums[i], + right = nums[j] * nums[j]; + if (left < right) { + res[k--] = right; + j--; + } else { + res[k--] = left; + i++; + } } - return res - } + return res; +}; ``` Swift: diff --git a/problems/算法模板.md b/problems/算法模板.md index 853816d2..69ebb361 100644 --- a/problems/算法模板.md +++ b/problems/算法模板.md @@ -460,7 +460,7 @@ var levelOrder = function (root) { for (let i = 0; i < n; i++) { let node = queue.shift(); temp.push(node.val); - node.left &&queue.push(node.left); + node.left && queue.push(node.left); node.right && queue.push(node.right); } res.push(temp);