diff --git a/problems/0222.完全二叉树的节点个数.md b/problems/0222.完全二叉树的节点个数.md index ba7acc5a..746d45cc 100644 --- a/problems/0222.完全二叉树的节点个数.md +++ b/problems/0222.完全二叉树的节点个数.md @@ -646,5 +646,68 @@ func countNodes(_ root: TreeNode?) -> Int { } ``` +## Scala + +递归: +```scala +object Solution { + def countNodes(root: TreeNode): Int = { + if(root == null) return 0 + 1 + countNodes(root.left) + countNodes(root.right) + } +} +``` + +层序遍历: +```scala +object Solution { + import scala.collection.mutable + def countNodes(root: TreeNode): Int = { + if (root == null) return 0 + val queue = mutable.Queue[TreeNode]() + var node = 0 + queue.enqueue(root) + while (!queue.isEmpty) { + val len = queue.size + for (i <- 0 until len) { + node += 1 + val curNode = queue.dequeue() + if (curNode.left != null) queue.enqueue(curNode.left) + if (curNode.right != null) queue.enqueue(curNode.right) + } + } + node + } +} +``` + +利用完全二叉树性质: +```scala +object Solution { + def countNodes(root: TreeNode): Int = { + if (root == null) return 0 + var leftNode = root.left + var rightNode = root.right + // 向左向右往下探 + var leftDepth = 0 + while (leftNode != null) { + leftDepth += 1 + leftNode = leftNode.left + } + var rightDepth = 0 + while (rightNode != null) { + rightDepth += 1 + rightNode = rightNode.right + } + // 如果相等就是一个满二叉树 + if (leftDepth == rightDepth) { + return (2 << leftDepth) - 1 + } + // 如果不相等就不是一个完全二叉树,继续向下递归 + countNodes(root.left) + countNodes(root.right) + 1 + } +} +``` + -----------------------
diff --git a/problems/0257.二叉树的所有路径.md b/problems/0257.二叉树的所有路径.md index 1362897c..70a3c66f 100644 --- a/problems/0257.二叉树的所有路径.md +++ b/problems/0257.二叉树的所有路径.md @@ -702,5 +702,35 @@ func binaryTreePaths(_ root: TreeNode?) -> [String] { } ``` +Scala: + +递归: +```scala +object Solution { + import scala.collection.mutable.ListBuffer + def binaryTreePaths(root: TreeNode): List[String] = { + val res = ListBuffer[String]() + def traversal(curNode: TreeNode, path: ListBuffer[Int]): Unit = { + path.append(curNode.value) + if (curNode.left == null && curNode.right == null) { + res.append(path.mkString("->")) // mkString函数: 将数组的所有值按照指定字符串拼接 + return // 处理完可以直接return + } + + if (curNode.left != null) { + traversal(curNode.left, path) + path.remove(path.size - 1) + } + if (curNode.right != null) { + traversal(curNode.right, path) + path.remove(path.size - 1) + } + } + traversal(root, ListBuffer[Int]()) + res.toList + } +} +``` + -----------------------
diff --git a/problems/0416.分割等和子集.md b/problems/0416.分割等和子集.md index eb6601e1..7347cd6f 100644 --- a/problems/0416.分割等和子集.md +++ b/problems/0416.分割等和子集.md @@ -417,6 +417,26 @@ var canPartition = function(nums) { ``` +TypeScript: + +```ts +function canPartition(nums: number[]): boolean { + const sum: number = nums.reduce((a: number, b: number): number => a + b); + if (sum % 2 === 1) return false; + const target: number = sum / 2; + // dp[j]表示容量(总数和)为j的背包所能装下的数(下标[0, i]之间任意取)的总和(<= 容量)的最大值 + const dp: number[] = new Array(target + 1).fill(0); + const n: number = nums.length; + for (let i: number = 0; i < n; i++) { + for (let j: number = target; j >= nums[i]; j--) { + dp[j] = Math.max(dp[j], dp[j - nums[i]] + nums[i]); + } + } + return dp[target] === target; +}; +``` + + C: 二维dp: ```c @@ -575,6 +595,5 @@ function canPartition(nums: number[]): boolean { - -----------------------
diff --git a/problems/0494.目标和.md b/problems/0494.目标和.md index 8ce1f6f1..0cdae393 100644 --- a/problems/0494.目标和.md +++ b/problems/0494.目标和.md @@ -351,22 +351,26 @@ const findTargetSumWays = (nums, target) => { }; ``` -TypeScript: -```typescript +TypeScript: + +```ts function findTargetSumWays(nums: number[], target: number): number { - const sum: number = nums.reduce((pre, cur) => pre + cur); - if (Math.abs(target) > sum) return 0; - if ((target + sum) % 2 === 1) return 0; - const bagSize: number = (target + sum) / 2; - const dp: number[] = new Array(bagSize + 1).fill(0); - dp[0] = 1; - for (let i = 0; i < nums.length; i++) { - for (let j = bagSize; j >= nums[i]; j--) { + // 把数组分成两个组合left, right.left + right = sum, left - right = target. + const sum: number = nums.reduce((a: number, b: number): number => a + b); + if ((sum + target) % 2 || Math.abs(target) > sum) return 0; + const left: number = (sum + target) / 2; + + // 将问题转化为装满容量为left的背包有多少种方法 + // dp[i]表示装满容量为i的背包有多少种方法 + const dp: number[] = new Array(left + 1).fill(0); + dp[0] = 1; // 装满容量为0的背包有1种方法(什么也不装) + for (let i: number = 0; i < nums.length; i++) { + for (let j: number = left; j >= nums[i]; j--) { dp[j] += dp[j - nums[i]]; } } - return dp[bagSize]; + return dp[left]; }; ``` diff --git a/problems/1049.最后一块石头的重量II.md b/problems/1049.最后一块石头的重量II.md index 3d256c3d..f3e7909c 100644 --- a/problems/1049.最后一块石头的重量II.md +++ b/problems/1049.最后一块石头的重量II.md @@ -277,26 +277,29 @@ var lastStoneWeightII = function (stones) { }; ``` -TypeScript: -```typescript +TypeScript版本 + +```ts function lastStoneWeightII(stones: number[]): number { - const sum: number = stones.reduce((pre, cur) => pre + cur); - const bagSize: number = Math.floor(sum / 2); - const weightArr: number[] = stones; - const valueArr: number[] = stones; - const goodsNum: number = weightArr.length; - const dp: number[] = new Array(bagSize + 1).fill(0); - for (let i = 0; i < goodsNum; i++) { - for (let j = bagSize; j >= weightArr[i]; j--) { - dp[j] = Math.max(dp[j], dp[j - weightArr[i]] + valueArr[i]); + const sum: number = stones.reduce((a: number, b:number): number => a + b); + const target: number = Math.floor(sum / 2); + const n: number = stones.length; + // dp[j]表示容量(总数和)为j的背包所能装下的数(下标[0, i]之间任意取)的总和(<= 容量)的最大值 + const dp: number[] = new Array(target + 1).fill(0); + for (let i: number = 0; i < n; i++ ) { + for (let j: number = target; j >= stones[i]; j--) { + dp[j] = Math.max(dp[j], dp[j - stones[i]] + stones[i]); } } - return sum - dp[bagSize] * 2; + return sum - dp[target] - dp[target]; }; ``` + + + -----------------------
diff --git a/problems/1365.有多少小于当前数字的数字.md b/problems/1365.有多少小于当前数字的数字.md index 78fa84c0..ce1e77df 100644 --- a/problems/1365.有多少小于当前数字的数字.md +++ b/problems/1365.有多少小于当前数字的数字.md @@ -217,6 +217,46 @@ var smallerNumbersThanCurrent = function(nums) { }; ``` +TypeScript: + +> 暴力法: + +```typescript +function smallerNumbersThanCurrent(nums: number[]): number[] { + const length: number = nums.length; + const resArr: number[] = []; + for (let i = 0; i < length; i++) { + let count: number = 0; + for (let j = 0; j < length; j++) { + if (nums[j] < nums[i]) { + count++; + } + } + resArr[i] = count; + } + return resArr; +}; +``` + +> 排序+hash + +```typescript +function smallerNumbersThanCurrent(nums: number[]): number[] { + const length: number = nums.length; + const sortedArr: number[] = [...nums]; + sortedArr.sort((a, b) => a - b); + const hashMap: Map = new Map(); + for (let i = length - 1; i >= 0; i--) { + hashMap.set(sortedArr[i], i); + } + const resArr: number[] = []; + for (let i = 0; i < length; i++) { + resArr[i] = hashMap.get(nums[i]); + } + return resArr; +}; +``` + -----------------------