消除重复元素

import java.util.*;
/**
 * 此题巧妙地用到了List去重的方法。
 * 比如说有一组数，为1 5 5 1 6 1
 * 从[0,n-1]使用List去重之后，保存地其实就是每种元素最开始出现的那个元素。
 * 但是我们换个角度去想，如果我们从后向前遍历，保存地就是每种元素最后出现的那个元素，只不过相对从前到后来说，数倒过来了。
 * 我们最终将数反转过来即可。
 * 时间复杂度为O(n)
 * @author 何嘉龙
 *
 */
public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		while(in.hasNext()) {
			int n = in.nextInt();
			int[] arr = new int[n];
			List<Integer> lists = new ArrayList<>();
			for(int i = 0; i < n; i++) {
				arr[i] = in.nextInt();
			}
			for(int i = n - 1; i >= 0; --i) {
				if(!lists.contains(arr[i])) {
					lists.add(arr[i]);
				}
			}
			for(int i = lists.size() - 1; i >= 0; --i) {
				System.out.print(lists.get(i));
				if(i != 0) {
					System.out.print(" ");
				}
			}
		}
		in.close();
	}
}

#include<iostream>
using namespace std;

int main ()
{
	int n;
	cin>>n;
	int seq[50];
	for(int i=0;i<n;i++)
	{
		cin>>seq[i];
	}
	
	for(int i=n-1;i>=0;i--)
	{
		int b=seq[i];
		for(int j=i-1;j>=0;j--)
		{
			if(b-seq[j]==0)
			{
				seq[j]=0;
			}
				
		}
	}
	for(int i=0;i<n;i++)
	{   if(seq[i]!=0)
		{
		cout<<seq[i];
        	if(i<(n-1))
                cout<<' ';
		}
		
	}
}

package go.jacob.day913;

import java.util.ArrayList;
import java.util.Scanner;

public class Demo3 {
	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		int n=sc.nextInt();
		int[] arr=new int[n];
		for(int i=0;i<n;i++){
			arr[i]=sc.nextInt();
		}
		ArrayList<Integer> res=new ArrayList<Integer>();
		for(int i=arr.length-1;i>=0;i--){
			if(!res.contains(arr[i]))
				res.add(arr[i]);
		}
		System.out.print(res.get(res.size()-1));
		for(int i=res.size()-2;i>=0;i--){
			System.out.print(" "+res.get(i));
		}
		sc.close();
	}
} 

import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

/**
 * @Author qgfzzzzzz
 * @Date 2019/8/19
 * @Version 1.0
 * <p>
 *
 * </p>
 */
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int[] arr = new int[n];
        Map<Integer, Integer> map = new HashMap<>();
        for(int i = 0; i < arr.length; i++){
            arr[i] = scanner.nextInt();
            map.put(arr[i], map.getOrDefault(arr[i], 0) + 1);
        }
        StringBuilder stringBuilder = new StringBuilder();
        for(int i = 0; i < arr.length; i++){
            if(map.get(arr[i]) == 1) stringBuilder.append(arr[i]).append(" ");
            else{
                int val = map.get(arr[i]);
                map.put(arr[i], val - 1);
            }
        }
        System.out.println(stringBuilder.toString().trim());
    }
}

#include<iostream>
#include<vector>
#include<set>
using namespace std;
int main()
{
	//数据输入
	int n;
	cin >> n;
	vector<int> sequence;
	for (int i = 0; i < n; i++)
	{
		int t;
		cin >> t;
		sequence.push_back(t);
	}
	//数据处理,利用set的值唯一特性
	set<int> temp;
	vector<int>result;
	for (int i = sequence.size()-1; i >=0; i--)
		if (temp.find(sequence[i])==temp.end())
		{
			temp.insert(sequence[i]);
			result.push_back(sequence[i]);
		}
	cout << result[result.size() - 1];
	for (int i = result.size() - 2; i >= 0; i--)	cout << " " << result[i];
    return 0;
}  

import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Scanner;

/**
*使用一个双端队列即可，比较简单，直接show the code
关键代码就五行
        Deque<Integer> q = new ArrayDeque<>();
        for (int i = n - 1; i >= 0; i --) {
            if (!q.contains(sequence[i])) {
                q.offerFirst(sequence[i]);
            }
        }
*/
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n  = sc.nextInt();
        int[] sequence = new int[n];
        for (int i = 0; i < n; i ++) {
            sequence[i] = sc.nextInt();
        }
        Deque<Integer> q = new ArrayDeque<>();
        for (int i = n - 1; i >= 0; i --) {
            if (!q.contains(sequence[i])) {
                q.offerFirst(sequence[i]);
            }
        }
        int count = q.size();
        for (int i = 0; i < count - 1; i ++) {
            System.out.print(q.poll() + " ");
        }
        System.out.println(q.poll());
    }
}

### 分析

从后向前先判重后加入即可。

### 我的答案

```cpp

#include<iostream>

#include<string>

#include<algorithm>

#include<set>

#include<vector>

using namespace std;

int main(){

    int n;

    int a[1002]={0};

    vector<int>v;

    set<int>s;

    cin>>n;

    for(int i=0;i<n;i++)

        cin>>a[i];

    for(int i=n-1;i>=0;i--){

        if(s.find(a[i])==s.end()){

            s.insert(a[i]);

            v.push_back(a[i]);

        }

    }

    cout<<v[v.size()-1];

    for(int i=v.size()-2;i>=0;i--){

        cout<<" "<<v[i];

    }

    cout<<endl;

```

https://blog.mythsman.com/2017/03/31/1/#消除重复元素

# -*- coding: UTF-8 -*-

#倒着读取，已有则不添加，再倒着打印即可。
import sys
n = int(raw_input().strip())
value=map(int,sys.stdin.readline().strip().split())
value.reverse()
i=0
arr=[]
while i<n:
    if value.index(value[i]) == i:
        arr.append(value[i])
    i=i+1
arr.reverse()
for x in arr:
	print x,

import java.util.*;

/*
 * 此题需要考虑从后往前遍历，可以使用map结构，针对不存在的情况才进行添加
 * */
public class RemoveDuplicateLast {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNext()) {
            int n = scanner.nextInt();
            int[] nums = new int[n];
            Map<Integer, Integer> map = new HashMap<>();
            List<Integer> list = new ArrayList<>();
            for (int i = 0; i < n; i++) {
                nums[i] = scanner.nextInt();
            }
            int index = 0;
            for (int i = n - 1; i >= 0; i--) {
//                不出现的情况才添加进来
                if (!map.containsKey(nums[i])) {
                    map.put(nums[i], 1);
                    list.add(nums[i]);
                    index++;
                }
            }
            System.out.print(list.get(index - 1));
            for (int i = index - 2; i >= 0; i--) {
                System.out.print(" " + list.get(i));
            }
            System.out.println();
        }
    }
}

import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] input = new int[n];
        for(int i = 0; i < n; i++)
            input[i] = sc.nextInt();
        int curP = n;
        Set<Integer> set = new HashSet<>();
        for(int i = n-1; i >= 0; i--) {
            if(set.add(input[i]))
                input[--curP] = input[i];
        }
        System.out.print(input[curP++]);
        for(; curP < n; )
            System.out.print(" " + input[curP++]);
        System.out.println();
    }
}

//对于array[i]使用倒叙list.contains()方法去重
//再反向输出list

import java.nio.charset.MalformedInputException;
import java.security.KeyStore.Entry;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Scanner;
import java.util.Set;
import java.util.Vector;

import javax.xml.transform.Templates;

public class Main{

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        /*
        9
        100 100 100 99 99 99 100 100 100
        */
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int [] array = new int [n];
        
        List<Integer> list = new ArrayList<>();
        
        for(int i = 0;i < n;i++){
            array[i] = scanner.nextInt();
            
        }
        
        for(int i = n-1;i >= 0;i--){
            if(list.contains(array[i]) == false){
                list.add(array[i]);
            }
        }
        System.out.print(list.get(list.size()-1));
        for(int i = list.size() - 2;i >= 0;i--){
            System.out.print(" " + list.get(i));
        }
        
        
    }

}

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        List<String> list=new ArrayList<>();
        for (int i = 0; i < n; i++) {
            String num=sc.next();
            if(list.contains(num)) list.remove(num);
            list.add(num);
        }
        for (int i=0;i<list.size();i++) {
            if(i!=list.size()-1){
                System.out.print(list.get(i)+" ");
            }else{
                System.out.println(list.get(i));
            }
        }
    }
}

#include<stdlib.h>
#include<stdio.h>
#include<string.h>
#include<unordered_map>
using namespace std;

void reomveOverLapStrs(const int* array, int n){
    unordered_map<int,int> map_;
    for(int ii=0;ii<n;ii++){
        map_[array[ii]]=ii;
    }
    for(int ii=0;ii<n;ii++){
        int index=map_[array[ii]];
        if(index==ii){
            if(ii==n-1)
                printf("%d\n",array[ii]);
            else
                printf("%d ",array[ii]);
        }
    }
}

int main(){
    int n=0;
    scanf("%d",&n);
    if(n<0 ||n>50)
        return -1;
    int *array=new int[n];
    for(int i=0;i<n;i++){
        scanf("%d",array+i);
        if(array[i]<0 || array[i]>1000)
            return -1;
    }
    
    reomveOverLapStrs(array, n);
    
    delete []array;
    return 0;
}