LeetCode刷题笔录Minimum Depth of Binary Tree

原创于 2014-07-13 00:57:09 发布 · 1k 阅读

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本文介绍了一种求解二叉树最小深度的有效算法。通过深度优先搜索（DFS）使用两个栈来遍历二叉树，找到从根节点到最近叶子节点的最短路径。此方法适用于所有类型的二叉树。

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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.

和Path Sum这题想法一样，DFS，两个Stack。

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int minDepth(TreeNode root) {
        Stack<TreeNode> nodeStack = new Stack<TreeNode>();
        Stack<Integer> depthStack = new Stack<Integer>();
        if(root == null)
            return 0;
        nodeStack.push(root);
        depthStack.push(1);
        int minDepth = Integer.MAX_VALUE;
        while(!nodeStack.isEmpty()){
            TreeNode node = nodeStack.pop();
            int currDepth = depthStack.pop();
            if(node.left == null && node.right == null){
                if(currDepth < minDepth)
                    minDepth = currDepth;
            }
            if(node.left != null){
                nodeStack.push(node.left);
                depthStack.push(currDepth + 1);
            }
            if(node.right != null){
                nodeStack.push(node.right);
                depthStack.push(currDepth + 1);
            }
        }
        return minDepth;
    }
}