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QOJ

IDProblemSubmitterResultTimeMemoryLanguageFile sizeSubmit timeJudge time
#556750#5981. Costly Binary SearchHkueen27 ✓11850ms86952kbC++142.0kb2024-09-10 20:33:082024-09-10 20:33:10

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你现在查看的是最新测评结果

  • [2024-09-10 20:33:10]
  • 评测
  • 测评结果:27
  • 用时:11850ms
  • 内存:86952kb
  • [2024-09-10 20:33:08]
  • 提交

answer

/*
如果所有c[i]都相等,那就是个二分查找
不相等的话,考虑暴力肯定就是区间dp了
设f[i][j]表示当前把x锁定在区间[i,j],最坏情况下还需要的最小代价
可以轻松得出转移:f[i][j]=min(c[k]+max(f[i][k-1],f[k+1][j]))
但是这样做O(n^3),肯定是不行的,时空都爆炸了。

考虑优化
显然,本题的入手点在于c[i]<=9
这意味着dp的值域很小,只有c*logn级别,上界只有180
而且这个dp很显然还有单调性,即若j<=k,f[i][j]<=f[i][k]
那我们就可以考虑用值域来记录dp状态
具体的,设L[j][c]表示区间的右端点在j,左端点最多延伸到L[j][c],有f[L[j][c]][j]<=c
同理设出R[i][c]
这个东西可以完全代替原来的dp数组,你考虑用它来做原来的转移
显然需要按照c从小到大来转移,所以我们考虑:
假设当前已经求出了所有的L[i][1~c-1]和R[i][1~c-1],我们如何算出L[i][c]和R[i][c]?
同样尝试去枚举中间的断点k,由于单调性,可以在枚举k的时候只更新离k最近的L和R,最后再推平L和R取前/后缀最优
时间复杂度O(n*c*logn)

空间爆炸了,但注意到我们只需要最多c-9的状态,于是可以滚动数组
*/
#include<bits/stdc++.h>
using namespace std;
constexpr int N=1e6+10;
char s[N];
int n,i,a[N],c,L[10][N],R[10][N];
int work(){
	scanf("%s",s+1);
	n=strlen(s+1);
	for(i=1;i<=n;++i)a[i]=(s[i]&15);
	for(c=0;c<181;++c){
		int zj=c%10;
		for(i=0;i<=n+1;++i)L[zj][i]=i+1,R[zj][i]=i-1;
		for(i=1;i<=n;++i){//枚举断点k
			if(c>=a[i]){
				int x=R[(c-a[i])%10][i+1],y=L[(c-a[i])%10][i-1];
				L[zj][x]=min(L[zj][x],y);
				R[zj][y]=max(R[zj][y],x);
			}
		}
		for(i=2;i<=n;++i)R[zj][i]=max(R[zj][i],R[zj][i-1]);
		for(i=n-1;i;--i)L[zj][i]=min(L[zj][i],L[zj][i+1]);
		if(L[zj][n]<=1||R[zj][1]>=n)return c;
	}
	puts("Didn't find the answer.");
	assert(0);
}
int T;
int main(){
	scanf("%d",&T);
	for(int z=1;z<=T;++z)printf("Case #%d: %d\n",z,work());
	return 0;
}

Details

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Subtask #1:

score: 8
Accepted

Test #1:

score: 8
Accepted
time: 80ms
memory: 46928kb

input:

50
8
5128831164925953487661279378526736416489768154389124821528467927357884749642747626797857463132866343496157991453139582295398452863172464853698678624523849653538713928372648295734165346972222781179687541337591976277864785653638476127839556323849395641196246971351933655287441377531627938395427487...

output:

Case #1: 8
Case #2: 37
Case #3: 34
Case #4: 37
Case #5: 34
Case #6: 114
Case #7: 126
Case #8: 24
Case #9: 37
Case #10: 103
Case #11: 36
Case #12: 64
Case #13: 37
Case #14: 117
Case #15: 37
Case #16: 35
Case #17: 14
Case #18: 34
Case #19: 36
Case #20: 37
Case #21: 38
Case #22: 39
Case #23: 14
Case #2...

result:

ok 50 lines

Subtask #2:

score: 19
Accepted

Test #2:

score: 19
Accepted
time: 11850ms
memory: 86952kb

input:

50
647322722753778843259213887674615134214258235986992692879314555957455541351526284343217116351733247781713552149464672262787737941588358671583528664757823365936975517145283412965139791726299864122725212222496898855627124979178341548651669956711341742838725446489235961853391195148929571712449139335...

output:

Case #1: 42
Case #2: 43
Case #3: 120
Case #4: 42
Case #5: 43
Case #6: 43
Case #7: 31
Case #8: 43
Case #9: 171
Case #10: 42
Case #11: 39
Case #12: 42
Case #13: 42
Case #14: 44
Case #15: 39
Case #16: 20
Case #17: 180
Case #18: 30
Case #19: 45
Case #20: 43
Case #21: 44
Case #22: 31
Case #23: 83
Case #2...

result:

ok 50 lines

Extra Test:

score: 0
Extra Test Passed