The array a with n integers is given. Let's call the sequence of one or more consecutive elements in a segment. Also let's call the segment k-good if it contains no more than k different values.
Find any longest k-good segment.
As the input/output can reach huge size it is recommended to use fast input/output methods: for example, prefer to use scanf/printfinstead of cin/cout in C++, prefer to use BufferedReader/PrintWriter instead of Scanner/System.out in Java.
The first line contains two integers n, k (1 ≤ k ≤ n ≤ 5·105) — the number of elements in a and the parameter k.
The second line contains n integers ai (0 ≤ ai ≤ 106) — the elements of the array a.
Print two integers l, r (1 ≤ l ≤ r ≤ n) — the index of the left and the index of the right ends of some k-good longest segment. If there are several longest segments you can print any of them. The elements in a are numbered from 1 to n from left to right.
5 5 1 2 3 4 5
1 5
9 3 6 5 1 2 3 2 1 4 5
3 7
3 1 1 2 3
1 1
two pointers一種不錯的編程技巧。
從前往後,或者從兩頭向中間,可使算法時間複雜度大大降低。
題目要求從所給序列找到一段儘量長的連續系列,使得這段序列不同數字個數(cnt)不大於K。
一個暴力的思路是:對於原始序列枚舉每個點作爲左端點,找到對應最大的右端點。記爲(Li,Ri)
假設從左向右邊枚舉,當枚舉Li+1時,先處理Li位置,然後,明顯當前Ri<=Ri+1;從Ri+1開始修改cnt值就可以了。
最後取最大值(Ri-Li)。
#include<cstdio>
#include<iostream>
#include<algorithm>
#include<queue>
#include<set>
#include<vector>
#include<time.h>
#include<string.h>
using namespace std;
#define LL __int64
#define N 1000005
int a[N],num[N];
int main()
{
int i,n,k;
int l,r,cnt,pos;
while(~scanf("%d%d",&n,&k)){
for(i=1;i<=n;++i){
scanf("%d",&a[i]);
}
l=r=1;
cnt=1;
pos=2;
memset(num,0,sizeof(num));
num[a[1]]=1;
for(i=1;i<=n;++i){
while(pos<=n&&cnt<=k){
++num[a[pos]];
if(num[a[pos]]==1){
++cnt;
}
if(cnt<=k)
++pos;
}
if(r-l<pos-1-i){
r=pos-1;
l=i;
}
--num[a[i]];
if(num[a[i]]==0){
--cnt;
++pos;
}
}
printf("%d %d\n",l,r);
}
return 0;
}