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

获取二叉树的最小深度，即最近的叶子节点的高度。由于存在子树为空需要舍弃的情况，因此先判断子树为空的话，返回另一子树的高度，否则返回两个子树的最低高度。

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
int minDepth(struct TreeNode* root) {
    if(root==NULL)
        return 0;
    if(root->left==NULL&&root->right==NULL)
        return 1;
    int leftDepth=1+minDepth(root->left);
    int rightDepth=1+minDepth(root->right);
    if(leftDepth==1)
        return rightDepth;
    if(rightDepth==1)
        return leftDepth;
    if(leftDepth>rightDepth)
        return rightDepth;
    else return leftDepth;
}