[Swift]LeetCode404. 左叶子之和 | Sum of Left Leaves

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Find the sum of all left leaves in a given binary tree.

Example:

    3
   / \
  9  20
    /  \
   15   7

There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.

---

计算给定二叉树的所有左叶子之和。

示例：

    3
   / \
  9  20
    /  \
   15   7

在这个二叉树中，有两个左叶子，分别是 9 和 15，所以返回 24

---

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public var val: Int
 *     public var left: TreeNode?
 *     public var right: TreeNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.left = nil
 *         self.right = nil
 *     }
 * }
 */
class Solution {
    var sum:Int = 0
    func sumOfLeftLeaves(_ root: TreeNode?) -> Int {
        if root == nil {return sum}
        if root!.left != nil
        {
            if root!.left!.left == nil && root!.left!.right == nil
            {
                sum += root!.left!.val
            }
        }
        //递归
        sumOfLeftLeaves(root!.left)
        sumOfLeftLeaves(root!.right)
        return sum
    }
}

---

12ms

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public var val: Int
 *     public var left: TreeNode?
 *     public var right: TreeNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.left = nil
 *         self.right = nil
 *     }
 * }
 */
class Solution {
    func sumOfLeftLeaves(_ root: TreeNode?) -> Int {
        return sumOfLeftLeaves(root, false)
    }
    
    func sumOfLeftLeaves(_ node: TreeNode?, _ isLeft: Bool) -> Int {
        guard let node = node else { return 0 }
        if node.left == nil && node.right == nil && isLeft {
            return node.val
        }
        
        return sumOfLeftLeaves(node.left, true) + sumOfLeftLeaves(node.right, false)
    }
}

---

16ms

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public var val: Int
 *     public var left: TreeNode?
 *     public var right: TreeNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.left = nil
 *         self.right = nil
 *     }
 * }
 */
class Solution {
    var sum = 0

    func sumOfLeftLeaves(_ root: TreeNode?) -> Int {
        if root == nil || (root?.left == nil && root?.right == nil) {
            return 0
        }
        
        search(root)
        
        return sum
    }
    
    func search(_ root: TreeNode?) -> Void {
        if root == nil {
            return
        }

        if isLeave(root?.left) {
            let val = root?.left?.val ?? 0
            sum = sum + val
        } else {
            search(root?.left)
        }
        
        if isLeave(root?.right) {
            return
        } else {
            search(root?.right)
        }
    }
    
    func isLeave(_ root: TreeNode?) -> Bool {
        if root == nil {
            return true
        }
        
        if root?.left == nil && root?.right == nil {
            return true
        }
        
        return false
    }
}

---

16ms

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public var val: Int
 *     public var left: TreeNode?
 *     public var right: TreeNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.left = nil
 *         self.right = nil
 *     }
 * }
 */
class Solution {
    func sumOfLeftLeaves(_ root: TreeNode?) -> Int {
        var result = 0
        sumOfLeftLeaves(root, &result)
        return result
    }
    
    func sumOfLeftLeaves(_ root: TreeNode?, _ sum: inout Int) {
        guard let root = root else {
            return
        }
        
        if let left = root.left {
            if left.left == nil && left.right == nil {
                sum += left.val
            } else {
                sumOfLeftLeaves(left, &sum)
            }
        }
        
        sumOfLeftLeaves(root.right, &sum)
    }
}

---

24ms

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public var val: Int
 *     public var left: TreeNode?
 *     public var right: TreeNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.left = nil
 *         self.right = nil
 *     }
 * }
 */
class Solution {
    func sumOfLeftLeaves(_ root: TreeNode?) -> Int {
            var sum = 0
            toSumLeftTreeNode(root: root, sum: &sum)
            return sum
        }
        func toSumLeftTreeNode(root: TreeNode?, sum: inout Int){
            if root == nil {
                return
            }
            if root?.left != nil && (root?.left?.left == nil && root?.left?.right == nil){
                sum = sum + (root?.left?.val)!
            }
            toSumLeftTreeNode(root: root?.left, sum: &sum)
            toSumLeftTreeNode(root: root?.right, sum: &sum)
        }
}