Minimum Depth of Binary Tree

Description

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.

Example
Given a binary tree as follow:
  1
 / \ 
2   3
   / \
  4   5
The minimum depth is 2.

Link

Lintcode_ladder

Method

1. BFS
2. x

Example

1. 1

/**
 * Definition of TreeNode:
 * class TreeNode {
 * public:
 *     int val;
 *     TreeNode *left, *right;
 *     TreeNode(int val) {
 *         this->val = val;
 *         this->left = this->right = NULL;
 *     }
 * }
 */
class Solution {
public:
    /**
     * @param root: The root of binary tree.
     * @return: An integer
     */
    int minDepth(TreeNode *root) {
        // write your code here
        if (!root) {
            return 0;
        }
        int count = 1;
        int depth = 0;
        queue<TreeNode*> q;
        q.push(root);
        while (!q.empty()) {
            TreeNode* cur = q.front();
            q.pop();
            count--;
            // find min shallow leaf node
            if (!cur->left && !cur->right) {
                return depth + 1;
            }
            // upadte q
            if (cur->left) {
                q.push(cur->left);
            }
            if (cur->right) {
                q.push(cur->right);
            }
            // update level summary
            if (count == 0) {
                count = q.size();
                ++depth;
            }
        }
        return -1;
    }
};

Similar problems

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Tags

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