17-比赛1 F - 较小元素 Weak in the Middle （set）

Seg-El has last chance to make the final changes in order to prevent the destruction of Krypton.

He is provided an array Arr[ ] of N elements.

For each element Arr [ i ], he needs to find the largest element Arr [ j ] where j < i and Arr [ j ] < Arr [ i ]

Help him to achieve this task.

Input

First line comprises N- the number of elements in the array.

Second line contains N space separated integers denoting the elements of the array.

Output

Print N lines denoting the required answer as specified above. In case no such value exists for some

Arr [ i ], print "-1" (without quotes).

Constraints

• 1 ≤ N ≤ 200000
• 1 ≤ Arr [ i ] ≤ 10¹⁵

Example

5 
1 2 3 5 4

Output:

-1 
1 
2 
3 
3

通过 set 或 map 就可轻松解决；

关键字 ：  set ，map ,  lower_bound()函数

1.学长的代码

 # include <bits/stdc++.h>
 using namespace std;
 set<long long> s;
 int main ()
 {
     int n;
     long long x;
     scanf("%d", &n);
     for (int i = ; i <= n; ++i) {
         scanf("%lld", &x);
         x = -x;
         auto iter = s.lower_bound(x + );
         if (iter == s.end()) puts("-1");
         else printf("%lld\n", -*iter);
         s.insert(x);
     }
     return ;
 }

2 . 一开始不会使用set ，用map自己做的

 #include<bits/stdc++.h>
 using namespace std;
 int main()
 {
     map<long long,int> imap;
     long long t;
     int n;
     cin>>n;
     for(int i =;i<=n;i++)
     {
         scanf("%lld",&t);
         t = -t;
         //map<long long,int>::iterator it;
         auto it = imap.lower_bound(t+);
         if(it == imap.end()) cout<<"-1"<<endl;
         else
            cout<<-(it->first)<<endl;
         imap[t] = i;
     }
     return ;
 }