PAT 1115 Counting Nodes in a BST (30)

A Binary Search Tree (BST) is recursively defined as a binary tree which has the following properties:

• The left subtree of a node contains only nodes with keys less than or equal to the node's key.
• The right subtree of a node contains only nodes with keys greater than the node's key.
• Both the left and right subtrees must also be binary search trees.

Insert a sequence of numbers into an initially empty binary search tree. Then you are supposed to count the total number of nodes in the lowest 2 levels of the resulting tree.

Input Specification:

Each input file contains one test case. For each case, the first line gives a positive integer N (<=1000) which is the size of the input sequence. Then given in the next line are the N integers in [-1000 1000] which are supposed to be inserted into an initially empty binary search tree.

Output Specification:

For each case, print in one line the numbers of nodes in the lowest 2 levels of the resulting tree in the format:

n1 + n2 = n

where n1 is the number of nodes in the lowest level, n2 is that of the level above, and n is the sum.

Sample Input:

9
25 30 42 16 20 20 35 -5 28

Sample Output:

2 + 4 = 6

题意：给你一个二叉树，让你找出最下面的那一层和倒数第二层的节点数

思路：直接用二叉树模板

代码：

#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <algorithm>
#include <queue>
#include <set>
#include <map>

using namespace std;

struct point {
    point *left;
    point *right;
    int val;
};
int n;
int cnt[1005];

void build(point *&root,int num) {
    if(root == NULL) {
        root = (point *)malloc(sizeof(point));
        root -> val = num;
        root->left = NULL;
        root->right = NULL;
        return;
    }
    if(root->val >= num) {
        build(root->left,num);
    } else {
        build(root->right,num);
    }
}
int sum1 = 0,sum2 = 0;
int maxdepth = -1;

void found(point *root,int dep) {
    if(root == NULL) {
        maxdepth = max(dep,maxdepth);
        return;
    }
    cnt[dep]++;
    found(root->left,dep+1);
    found(root->right,dep+1);
}
int main() {
    cin >> n;
    point *root = NULL;
    int a;
    for(int i = 0; i < n; i++) {
        cin >> a;
        build(root,a);
    }
    found(root,0);
    printf("%d + %d = %d\n",cnt[maxdepth-1],cnt[maxdepth-2],cnt[maxdepth-1]+cnt[maxdepth-2]);
    return 0;
}