Minimum Depth of Binary Tree

描述

Given a binary tree, find its minimum depth.

The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.

分析

无

递归版

  1. // Minimum Depth of Binary Tree
  2. // 递归版，时间复杂度O(n)，空间复杂度O(logn)
  3. class Solution {
  4. public:
  5.     int minDepth(const TreeNode *root) {
  6.         return minDepth(root, false);
  7.     }
  8. private:
  9.     static int minDepth(const TreeNode *root, bool hasbrother) {
  10.         if (!root) return hasbrother ? INT_MAX : 0;
  12.         return 1 + min(minDepth(root->left, root->right != NULL),
  13.                 minDepth(root->right, root->left != NULL));
  14.     }
  15. };

迭代版

  1. // Minimum Depth of Binary Tree
  2. // 迭代版，时间复杂度O(n)，空间复杂度O(logn)
  3. class Solution {
  4. public:
  5.     int minDepth(TreeNode* root) {
  6.         if (root == nullptr)
  7.             return 0;
  9.         int result = INT_MAX;
  11.         stack<pair<TreeNode*, int>> s;
  12.         s.push(make_pair(root, 1));
  14.         while (!s.empty()) {
  15.             auto node = s.top().first;
  16.             auto depth = s.top().second;
  17.             s.pop();
  19.             if (node->left == nullptr && node->right == nullptr)
  20.                 result = min(result, depth);
  22.             if (node->left && result > depth) // 深度控制，剪枝
  23.                 s.push(make_pair(node->left, depth + 1));
  25.             if (node->right && result > depth) // 深度控制，剪枝
  26.                 s.push(make_pair(node->right, depth + 1));
  27.         }
  29.         return result;
  30.     }
  31. };

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原文: https://soulmachine.gitbooks.io/algorithm-essentials/content/cpp/binary-tree/recursion/minimum-depth-of-binary-tree.html