codeforces Educational Codeforces Round 49 (Rated for Div. 2) C题

刚开始拿到这题很懵逼，知道了别人的思路之后开始写，但是还是遇到很多坑，要求求P^2/S最大。p=a b。就是求（a²+ b² +2ab)/ab最大，也就是a/b +b/a最大。那么题意就很明显了。
但是处理的时候还要注意，刚开始用map存入数据，保存数量大于2的数据。接着就是找最小的，千万不要用数组进行双重循环查找，这样的O（n*n）会爆时，要先排序O(lgn);然后对相邻的遍历比较一遍就可以了O（n）。当数据量很大的时候差距很明显。
附上ac代码（java）

package codeforces504;import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.StreamTokenizer;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
/** 贪心 数学 排序*/
public class testC {public static void main(String[] args) throws IOException {// TODO 自动生成的方法存根StreamTokenizer in=new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));in.nextToken();int n=(int)in.nval;for(int i=0;i<n;i++){in.nextToken();int num=(int)in.nval;int a[]=new int[num];Map<Integer,Integer>map=new HashMap();     for(int j=0;j<num;j++){in.nextToken();int q=(int)in.nval;if(map.containsKey(q)) {map.put(q, map.get(q)+1);}else map.put(q, 1);}int index=0;int a2=0;int b2=0;boolean b=false;for(int q:map.keySet()){if(map.get(q)>=4) {a2=q;b2=q;b=true;break;}elseif(map.get(q)>=2) {a[index++]=q;}}if(!b) {Arrays.sort(a,0, index);//0-到index-1排序      double min=Double.MAX_VALUE;;for(int q=0;q<index-1;q++){double d=(double)a[q]/(double)a[q+1]+(double)a[q+1]/(double)a[q];if(d<min) {min=d;a2=a[q];b2=a[q+1];}         }}out.println(a2+" "+a2+" "+b2+" "+b2);out.flush();}}
}

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codeforces Educational Codeforces Round 49 (Rated for Div. 2) C题

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