你可不可以
成为我的main函数
做我此生必须有
且只能有一个的入口
——————————
我愿为自己加上private
在你的class中只有
你能调用
——————————————代 码 如 诗 。
Given two binary trees, write a function to check if they are equal or not.
Two binary trees are considered equal if they are structurally identical and the nodes have the same value.
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if let p = p, let q = q { return p.val == q.val && isSameTree(p.left, q.left) && isSameTree(p.right, q.right) } else { return p == nil && q == nil } |
Given a binary tree, determine if it is a valid binary search tree (BST).
Assume a BST is defined as follows:
The left subtree of a node contains only nodes with keys less than the node’s key.
The right subtree of a node contains only nodes with keys greater than the node’s key.
Both the left and right subtrees must also be binary search trees.
Example 1:
2
/ \
1 3
Binary tree [2,1,3], return true.
Example 2:
1
/ \
2 3
Binary tree [1,2,3], return false.
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func isValidBST(_ root: TreeNode?) -> Bool { return isValidNode(root, Int.min, Int.max) } private func isValidNode(_ root: TreeNode?, _ min: Int, _ max: Int) -> Bool { guard let p = root else { return true } if p.val >= max || p.val <= min { return false } return isValidNode(p.left, min, p.val) && isValidNode(p.right, p.val, max) } |
Given n, how many structurally unique BST’s (binary search trees) that store values 1…n?
For example,
Given n = 3, there are a total of 5 unique BST’s.
1 3 3 2 1
\ / / / \ \
3 2 1 1 3 2
/ / \ \
2 1 2 3
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func numTrees(_ n: Int) -> Int { list = Array(repeating: 1, count: n+1) if n >= 2 { list[2] = 2 } return g(n) } private var list: [Int]! private func g(_ n: Int) -> Int { if n > 2 && list[n] == 1 { list[n] = (1...n).reduce(0) { $0 + f($1, n) } } return list[n] } private func f(_ i: Int, _ n: Int) -> Int { return g(i-1) * g(n-i) } |
Given a binary tree, return the inorder traversal of its nodes’ values.
For example:
Given binary tree [1,null,2,3],
1
\
2
/
3
return [1,3,2].
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func inorderTraversal(_ root: TreeNode?) -> [Int] { var list = [Int](), stack = [TreeNode](), p = root while p != nil || !stack.isEmpty { if let t = p { stack.append(t) p = t.left } else { let t = stack.popLast()! list.append(t.val) p = t.right } } return list } |
Given an array with n objects colored red, white or blue, sort them so that objects of the same color are adjacent, with the colors in the order red, white and blue.
Here, we will use the integers 0, 1, and 2 to represent the color red, white, and blue respectively.
Note:
You are not suppose to use the library’s sort function for this problem.
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func sortColors(_ nums: inout [Int]) { var i0 = 0, i1 = 0, i2 = nums.count-1 while i1 <= i2 { if nums[i1] == 2 { nums.swapAt(i1, i2) i2 -= 1 } else if nums[i1] == 0 { nums.swapAt(i0, i1) i0 += 1; i1 += 1 } else { i1 += 1 } } } |
You are climbing a stair case. It takes n steps to reach to the top.
Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?
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func climbStairs(_ n: Int) -> Int { if n < 4 { return n } var arr = Array(repeating: 1, count: n+1) arr[2] = 2; arr[3] = 3 for i in (4...n) { arr[i] = arr[i-1] + arr[i-2] } return arr[n] } |