前端树的相关算法

前端树的相关算法

树的遍历要结合栈的思想 示例代码：

let tree = {
  val: '1',
  left: {
    val: '2',
    left: {
      val: '4',
    },
    right: {
      val: '3',
    },
  },
  right: {
    val: '5',
    right: {
      val: '6',
    },
  },
}

树的深度优先遍历

let dfs = (root) => {
  if (!root) {
    return
  }
  consloe.log(root.val)
  if (root.left) dfs(root.left)
  if (root.right) dfs(root.right)
}

树的广度优先遍历

let bfs = (root) => {
  if (!root) {
    return
  }
  let p = [root]
  while (p.length) {
    let n = p.shift()
    if (n.left) p.push(n.left)
    if (n.right) p.push(n.right)
  }
}

树的先序遍历（根左右）

//递归解法
let preInorder = (root) => {
  if (!root) {
    return
  }
  console.log(root.val)
  preInorder(root.left)
  preInorder(root.right)
}
//栈解法
let preInorder = (root) => {
  if (!root) {
    return
  }
  let stack = [root]
  while (stack.length) {
    let n = stack.pop()
    console.log(n.val)
    if (n.right) stack.push(n.right)
    if (n.left) stack.push(n.left)
  }
}

树的中序遍历（左根右）

//递归解法
let inInorder = (root) => {
  if (!root) {
    return
  }
  inInorder(root.left)
  console.log(root.val)
  inInorder(root.right)
}

//栈解法
let inInorder = (root) => {
  if (!root) {
    return
  }
  let stack = []
  let p = root
  while (stack.length || p) {
    while (p) {
      stack.push(p)
      p = p.left
    }
    const n = stack.pop()
    console.log(n.val)
    p = n.right
  }
}

树的后序遍历（左右根）

//递归解法
let downInorder = (root) => {
  if (!root) {
    return
  }
  downInorder(root.left)
  downInorder(root.right)
  console.log(root.val)
}

//栈解法
let downInorder = (root) => {
  if (!root) {
    return
  }
  let stack = [root]
  let outputStack = []
  while (stack.length) {
    const n = stack.pop()
    outputStack.push(n)
    if (n.left) stack.push(n.left)
    if (n.right) stack.push(n.right)
  }
  while (outputStack.length) {
    const n = outputStack.pop()
    console.log(n.val)
  }
}