BFS 算法解题套路框架

问题的本质就是让你在一幅「图」中找到从起点 start 到终点 target 的最近距离，这个例子听起来很枯燥，但是 BFS 算法问题其实都是在干这个事儿

/**
 * 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)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
var minDepth = function (root) {
  // bfs
  if (!root) return 0
  const queue = []
  let res = 1

  queue.push(root)

  while (queue.length) {
    const sz = queue.length
    for (let i = 0; i < sz; i++) {
      let cur = queue.shift()

      if (cur.left === null && cur.right === null) {
        return res
      }
      if (cur.left) {
        queue.push(cur.left)
      }
      if (cur.right) {
        queue.push(cur.right)
      }
    }

    res += 1
  }
}