839:Not so Mobile

Not so Mobile

 

我的思路：可以将天平看做一棵二叉树，二叉树的每个节点要记录其父节点。然后其实就是一个建树的过程，遇到 0 节点就向下延伸，每当一个节点的左右子树确定（其重量也随之确定），就计算其是否平衡，然后一直向上追溯，直到该节点尚未平衡，继续建树，直至整棵树建好，是否平衡也随之确定。

version 1(40ms):

#include<bits/stdc++.h>
using namespace std;
const int maxn = 10000 + 5;
int t,wl,dl,wr,dr;
struct node{
    int w = 0,d = 0;
    struct node* dad = NULL;
    struct node* left = NULL;
    struct node* right = NULL;
};
node* newnode(){ return new node; }
void build_tree(int& mark){
    node* root = newnode();
    node* t = root;
    while(!root->w){
        scanf("%d%d%d%d",&wl,&dl,&wr,&dr);
        if(!t->left){
            t->left = newnode();
            t->left->w = wl;
            t->left->d = dl;
            t->left->dad = t;
        }
        if(!t->right){
            t->right = newnode();
            t->right->w = wr;
            t->right->d = dr;
            t->right->dad = t;
        }
        if(t->left->w && t->right->w){
            while(t->left->w && t->right->w){
                t->w = t->left->w + t->right->w;
                if(mark && t->left->w*t->left->d != t->right->w*t->right->d) mark = 0;
                if(t == root) break;
                t = t->dad;
            }
            t = (!t->left->w ? t->left : t->right);
        }
        else if(!t->left->w) t = t->left;
        else t = t->right;
    }
}
int main(){
    // freopen("data.in","r",stdin);
    // freopen("data.out","w",stdout);
    scanf("%d",&t);
    while(t--){
        int mark = 1;
        build_tree(mark);
        printf("%s\n",mark ? "YES" : "NO");
        if(t) putchar('\n');
    }
    return 0;
}

看了看书上的代码，直接递归就行。。。既简洁又优美。智商的差距。。。

version 2(20ms):

#include<bits/stdc++.h>
using namespace std;
const int maxn = 10000 + 5;
int t,w;
bool solve(int& w){
    int wl,dl,wr,dr;
    scanf("%d%d%d%d",&wl,&dl,&wr,&dr);
    int bl = 1,br = 1;
    if(!wl) bl = solve(wl);
    if(!wr) br = solve(wr);
    w = wl + wr;
    return bl && br && wl*dl == wr*dr;
}
int main(){
    // freopen("data.in","r",stdin);
    // freopen("data.out","w",stdout);
    scanf("%d",&t);
    while(t--){
        printf("%s\n",solve(w) ? "YES" : "NO");
        if(t) putchar('\n');
    }
    return 0;
}