Find Leaves of Binary Tree

Description

null

Solution(javascript)

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
// /** 1: parent pointer + BFS
//  * @param {TreeNode} root
//  * @return {number[][]}
//  */
// const findLeaves = function (root) {
//   const parent = new Map()
//   let current = []
//   const visited = new Map()
//   const isLeaf = node => !node.left && !node.right
//   const aux = (node, parentNode = null) => {
//     if (!node) {
//       return
//     }
//     if (isLeaf(node)) {
//       current.push(node)
//       visited.set(node, true)
//     }
//     parent.set(node, parentNode)
//     aux(node.left, node)
//     aux(node.right, node)
//   }
//   aux(root)
//   const result = []
//   while (current.length > 0) {
//     const next = []
//     result.push(current.map(node => node.val))
//     for (const node of current) {
//       const parentNode = parent.get(node)
//       if (parentNode) {
//         if (parentNode.left === node) {
//           parentNode.left = null
//         } else {
//           parentNode.right = null
//         }
//         if (isLeaf(parentNode) && !visited.get(parentNode)) {
//           next.push(parentNode)
//           visited.set(parentNode, true)
//         }
//       }
//     }
//     current = next
//   }
//   return result
// }


/** 2: 根据 depth 来解决
 * @param {TreeNode} root
 * @return {number[][]}
 */
const findLeaves = function (root) {
  const result = []
  const aux = (node) => {
    if (!node) {
      return -1
    }
    const depth = 1 + Math.max(aux(node.left), aux(node.right))
    result[depth] = result[depth] || []
    result[depth].push(node.val)
    return depth
  }
  aux(root)
  return result
}