习题5-6 对称轴 UVa1595

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1.题目描述：点击打开链接

2.解题思路：判断是否对称只需要看x坐标，因此可以先将每个y值分配一个ID；先判断是否自对称，如果都是，进一步判断所有自对称的对称轴是否都相同，注意用对称轴坐标的二倍来判断，尽量避免浮点数的使用。

3.代码：

#define _CRT_SECURE_NO_WARNINGS#include<iostream>#include<algorithm>#include<string>#include<sstream>#include<set>#include<vector>#include<stack>#include<map>#include<queue>#include<cassert>#include<cstdlib>#include<ctime>#include<cmath>#include<cstring>#include<functional>using namespace std;const int maxn = 1000 + 10;vector<int>dot[maxn];vector<int>arr;map<int,int>yid;int sym[maxn];int ID(int y){if (yid.count(y))return yid[y];else{arr.push_back(y);yid[y] = arr.size() - 1;return yid[y];}}bool is_sym(int p){int len = dot[p].size();if (len == 1 || len == 2) return true;else if (len % 2){int mid = len / 2;int x = dot[p][mid] * 2;for (int i = 0; i < mid;i++)if (dot[p][i] + dot[p][len - i - 1] != x)return false;return true;}else{int mid = len / 2;int x = dot[p][0] + dot[p][len - 1];for (int i = 0; i < mid;i++)if (dot[p][i] + dot[p][len - 1 - i] != x)return false;return true;}}int main(){int T;cin >> T;while (T--){int n;int flag = 1;memset(sym, 0, sizeof(sym));arr.clear();yid.clear();for (int i = 0; i < maxn; i++)dot[i].clear();cin >> n;for (int i = 0; i < n; i++){int x, y;cin >> x >> y;dot[ID(y)].push_back(x);}int len = arr.size();for (int i = 0; i < len; i++)sort(dot[i].begin(), dot[i].end());for (int i = 0; i < len;i++)if (!is_sym(i)){flag = 0;break;}elsesym[i] = dot[i][0] + dot[i][dot[i].size() - 1];if (flag){int x = sym[0];for (int i = 0; i < len;i++)if (sym[i] != x){flag = 0;break;}}if (flag)cout << "YES" << endl;elsecout << "NO" << endl;}return 0;}

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