B
来源:互联网 发布:韩礼德 知乎 编辑:程序博客网 时间:2024/04/27 16:42
Description
A permutation of length n is an integer sequence such that each integer from 0 to (n - 1) appears exactly once in it. For example, sequence [0, 2, 1] is a permutation of length 3 while both [0, 2, 2] and [1, 2, 3] are not.
A fixed point of a function is a point that is mapped to itself by the function. A permutation can be regarded as a bijective function. We'll get a definition of a fixed point in a permutation. An integer i is a fixed point of permutation a0, a1, ..., an - 1 if and only if ai = i. For example, permutation [0, 2, 1] has 1 fixed point and permutation [0, 1, 2] has 3 fixed points.
You are given permutation a. You are allowed to swap two elements of the permutation at most once. Your task is to maximize the number of fixed points in the resulting permutation. Note that you are allowed to make at most one swap operation.
Input
The first line contains a single integer n(1 ≤ n ≤ 105). The second line contains n integers a0, a1, ..., an - 1 — the given permutation.
Output
Print a single integer — the maximum possible number of fixed points in the permutation after at most one swap operation.
Sample Input
50 1 3 4 2
3
如果i=a[i]那么i就是一个 固定点,最多交换一次位置,取得最多的固定点
分析:
将不是固定点的放在一起map里,找关键字,看是否符合
代码:
#include<bits/stdc++.h>using namespace std;int main(){ int n,i,a[100005],s,p,t,o; map<int,int>v; map<int,int>::iterator it1,it2; while(cin>>n) { for(i=0,s=0,t=0,o=0,p=0;i<n;i++) { cin>>a[i]; if(a[i]!=i) { v.insert(make_pair(i,a[i])); t=1; } else s++; } while(!v.empty()) { it2=v.begin(); it1=v.find((*it2).second); if(it1!=v.end()) { o=1; if((*it2).first==(*it1).second) { p=1; break; } else { v.erase(it2); v.erase(it1); } } else v.erase(it2); } v.clear(); if(p) cout<<s+2<<endl; else if(o) cout<<s+1<<endl; else cout<<s<<endl; }}
感受:
其实可以不用map,map还是费事,其实存数组了就好
- b
- b
- b
- //b
- B
- b
- B
- B
- B
- B
- b
- B
- B
- B
- B
- B
- B
- b
- Linux-Ubuntu 命令总结
- Android 内外部存储,file存储
- android 禁用多点触摸
- 关于在Eclipse中Could not locate executabl ....\hadoop-2.2.0\hadoop-2.2.0\bin\winutils.exe in the Hadoo
- DialogUtils(material风格,ios风格,传入context构建,在任意界面弹出,以及dialog样式的activity)
- B
- Java web 项目中文件路径
- python使用pip安装一个module时报错:RuntimeError: maximum recursion depth exceeded
- 根据先序,中序求一棵树
- 关于Struts2和ajax的登录验证问题
- delphi oracle odac
- hdfs回顾总结(3)---使用hadoopRpc模拟namenode元数据的查询
- Kotlin的属性委托:无上下文情况下Android的赋值(KAD 15)
- jsp静态化和伪静态化《转载》