用于找从起点start到终点target的最近距离

    1. /**
    2.  * Definition for a binary tree node.
    3.  * struct TreeNode {
    4.  *     int val;
    5.  *     TreeNode *left;
    6.  *     TreeNode *right;
    7.  *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
    8.  *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
    9.  *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
    10.  * };
    11.  */
    12. class Solution {
    13. public:
    14.     int minDepth(TreeNode* root) {
    15.         if(root == nullptr)
    16.             return 0;
    17.         queue<TreeNode *> q;
    18.         q.push(root);
    19.         int minDeep = 1;
    21.         while(!q.empty())
    22.         {
    23.             int len = q.size();
    24.             for(int i = 0; i < len; i++)
    25.             {
    26.                 TreeNode* Node = q.front();
    27.                 q.pop();
    29.                 if(Node->right == nullptr && Node->left == nullptr)
    30.                     return minDeep;
    31.                 if(Node->right != nullptr)
    32.                     q.push(Node->right);
    33.                 if(Node->left != nullptr)
    34.                     q.push(Node->left);
    35.             }
    36.             minDeep++;
    37.         }
    38.         return minDeep;
    39.     }
    40. };