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C++实现LeetCode(104.二叉树的最大深度)

程序员文章站 2022-06-23 10:49:31
[leetcode] 104. maximum depth of binary tree 二叉树的最大深度given a binary tree, find its maximum depth.the...

[leetcode] 104. maximum depth of binary tree 二叉树的最大深度

given a binary tree, find its maximum depth.

the maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

note: a leaf is a node with no children.

example:

given binary tree [3,9,20,null,null,15,7],

    3
/ \
9  20
/  \
15   7

return its depth = 3.

求二叉树的最大深度问题用到深度优先搜索 depth first search,递归的完美应用,跟求二叉树的最小深度问题原理相同,参见代码如下:

c++ 解法一:

class solution {
public:
    int maxdepth(treenode* root) {
        if (!root) return 0;
        return 1 + max(maxdepth(root->left), maxdepth(root->right));
    }
};

java 解法一:

public class solution {
    public int maxdepth(treenode root) {
        return root == null ? 0 : (1 + math.max(maxdepth(root.left), maxdepth(root.right)));
    }
}

我们也可以使用层序遍历二叉树,然后计数总层数,即为二叉树的最大深度,注意 while 循环中的 for 循环的写法有个 trick,一定要将 q.size() 放在初始化里,而不能放在判断停止的条件中,因为q的大小是随时变化的,所以放停止条件中会出错,参见代码如下:

c++ 解法二:

class solution {
public:
    int maxdepth(treenode* root) {
        if (!root) return 0;
        int res = 0;
        queue<treenode*> q{{root}};
        while (!q.empty()) {
            ++res;
            for (int i = q.size(); i > 0; --i) {
                treenode *t = q.front(); q.pop();
                if (t->left) q.push(t->left);
                if (t->right) q.push(t->right);
            }
        }
        return res;
    }
};

java 解法二:

public class solution {
    public int maxdepth(treenode root) {
        if (root == null) return 0;
        int res = 0;
        queue<treenode> q = new linkedlist<>();
        q.offer(root);
        while (!q.isempty()) {
            ++res;
            for (int i = q.size(); i > 0; --i) {
                treenode t = q.poll();
                if (t.left != null) q.offer(t.left);
                if (t.right != null) q.offer(t.right);
            }
        }
        return res;
    }
}

github 同步地址:

类似题目:

balanced binary tree

minimum depth of binary tree

maximum depth of n-ary tree

参考资料:

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