PAT(A) 1110. Complete Binary Tree (25)

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原题目：

原题链接：https://www.patest.cn/contests/pat-a-practise/1110

1110. Complete Binary Tree (25)

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Given a tree, you are supposed to tell if it is a complete binary tree.

Input Specification:

Each input file contains one test case. For each case, the first line gives a positive integer N (<=20) which is the total number of nodes in the tree – and hence the nodes are numbered from 0 to N-1. Then N lines follow, each corresponds to a node, and gives the indices of the left and right children of the node. If the child does not exist, a “-” will be put at the position. Any pair of children are separated by a space.

Output Specification:

For each case, print in one line “YES” and the index of the last node if the tree is a complete binary tree, or “NO” and the index of the root if not. There must be exactly one space separating the word and the number.

Sample Input 1:
9
7 8
- -
- -
- -
0 1
2 3
4 5
- -
- -
Sample Output 1:
YES 8
Sample Input 2:
8
- -
4 5
0 6
- -
2 3
- 7
- -
- -
Sample Output 2:
NO 1

题目大意

给N个节点，并告知每个节点的左右节点，若是‘-’表示节点为空。判断是否为完全二叉树。若是，输出YES和最后一个节点的值。若不是，输出NO和根节点的值。

解题报告

读入，建树，并用visit标记是否为子节点。
做的时候碰到个坑，没注意到节点数范围，单纯认为0-9，用char读入，结果出问题。

代码

/*
* Problem: 1110. Complete Binary Tree (25)
* Author: HQ
* Time: 2018-03-10
* State: Done
* Memo:　完全二叉树的建立及检验。
*/
#include "iostream"
#include "string"
#include "vector"
using namespace std;
string node[20 + 2][2];
bool visit[20 + 2] = { false };
int tree[20 + 2];
bool flag = true;

int N;

void makeTree(int pos, int x) {
    if (pos > N || x >= N) {
        return;
    }
    tree[pos] = x;
    if (flag && node[x][0][0] != '-')
        makeTree(pos * 2, stoi(node[x][0]));
    if (flag && node[x][1][0] != '-')
        makeTree(pos * 2 + 1, stoi(node[x][1]));
}

int main() {
    cin >> N;
    for (int i = 0; i < N; i++) {
        cin>>node[i][0]>>node[i][1];
        if (node[i][0][0] != '-') {
            visit[stoi(node[i][0])] = true;
        }
        if (node[i][1][0] != '-') {
            visit[stoi(node[i][1])] = true;
        }
    }
    fill(tree, tree+N+1, -1);
    int i;
    for (i = 0; i < N; i++) {
        if (!visit[i])
            break;
    }
    makeTree(1, i);
    for(int j = 1; j <= N; j++)
        if (tree[j] == -1) {
            printf("NO %d\n", i);
            flag = false;
            break;
        }
    if(flag)
        printf("YES %d\n", tree[N]);
    system("pause");
}