513.找树左下角的值.md

513.找树左下角的值

/*
 * @lc app=leetcode.cn id=513 lang=typescript
 *
 * [513] 找树左下角的值
 */

// @lc code=start
/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     val: number
 *     left: TreeNode | null
 *     right: TreeNode | null
 *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.left = (left===undefined ? null : left)
 *         this.right = (right===undefined ? null : right)
 *     }
 * }
 */

function findBottomLeftValue(root: TreeNode | null): number {}
// @lc code=end

解法 1: DFS

function findBottomLeftValue(root: TreeNode | null): number {
  if (!root) return -1
  let res = 0,
    left = Infinity,
    bottom = -Infinity
  const dfs = (node: TreeNode, l = 0, b = 0) => {
    if (bottom === b) {
      if (left > l) {
        res = node.val
        left = l
        bottom = b
      }
    } else if (bottom < b) {
      res = node.val
      left = l
      bottom = b
    }
    if (node.left) {
      dfs(node.left, l - 1, b + 1)
    }
    if (node.right) {
      dfs(node.right, l + 1, b + 1)
    }
  }
  dfs(root)
  return res
}