PAT--1110. Complete Binary Tree

link to problem

题解

• 主要是构建树，用数组来存储的话很容易判断是不是完全二叉树。
• 找出根节点然后递归构造。

#include <iostream>#include <cstdio>#include <algorithm>#include <cstring>#include <cstdlib>using namespace std;const int maxn = 100;struct node{    int left, right;};int n;int tree[maxn];node a[maxn];int appear[maxn];void build(int root, int t){    if(root == -1) return;    tree[t] = root;    build(a[root].left,  t*2 + 1);    build(a[root].right, t*2 + 2);}int main(){#ifndef ONLINE_JUDGEfreopen("data.in", "r", stdin);#endif // ONLINE_JUDGE    cin >> n;    string s1, s2;    for(int i = 0; i < n; ++i){        cin >> s1 >> s2;        a[i].left  = (s1 == "-") ? -1 : atoi(s1.c_str());        a[i].right = (s2 == "-") ? -1 : atoi(s2.c_str());        if(a[i].left  != -1) appear[a[i].left]  = true;        if(a[i].right != -1) appear[a[i].right] = true;    }    int root = -1;    for(int i = 0; i < n; ++i){        if(!appear[i]){            root = i;            break;        }    }    memset(tree, -1, sizeof(tree));    build(root, 0);    bool ans = true;    for(int i = 0; i < n; ++i){        if(tree[i] == -1){            ans = false;            break;        }    }    if(ans) printf("YES %d\n", tree[n - 1]);    else printf("NO %d\n", tree[0]);    return 0;}