HDU 6047 Maximum Sequence【贪心】
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题目来戳呀
Problem Description
Steph is extremely obsessed with “sequence problems” that are usually seen on magazines: Given the sequence 11, 23, 30, 35, what is the next number? Steph always finds them too easy for such a genius like himself until one day Klay comes up with a problem and ask him about it.
Given two integer sequences {ai} and {bi} with the same length n, you are to find the next n numbers of {ai}: an+1…a2n. Just like always, there are some restrictions on an+1…a2n: for each number ai, you must choose a number bk from {bi}, and it must satisfy ai≤max{aj-j│bk≤j
Input
The input contains no more than 20 test cases.
For each test case, the first line consists of one integer n. The next line consists of n integers representing {ai}. And the third line consists of n integers representing {bi}.
1≤n≤250000, n≤a_i≤1500000, 1≤b_i≤n.
Output
For each test case, print the answer on one line: max{∑2nn+1ai} modulo 109+7。
Sample Input
4
8 11 8 5
3 1 4 2
Sample Output
27
Hint
For the first sample:
1. Choose 2 from {bi}, then a_2…a_4 are available for a_5, and you can let a_5=a_2-2=9;
2. Choose 1 from {bi}, then a_1…a_5 are available for a_6, and you can let a_6=a_2-2=9;
题意:
长度为n的a和b数列,想要将a后添加n个元素,添加的a数列满足
想法:
为了使新增的每一个a
所以我们先从后往前更新a
最后再取a
tips:
1.a,b数组开的时候要注意是开两倍,因为增加了n个元素
2.在最后取a
#include<cstdio>#include<algorithm>#include<cstring>#include<cmath>using namespace std;int a[510000],b[510000];//数组范围要注意const int mod=1e9+7;int main(){ int maxn,n; while(~scanf("%d",&n)) { maxn=-mod; for(int i=1;i<=n;++i) { scanf("%d",&a[i]); a[i]=a[i]-i; } for(int i=n;i>=1;--i) {//从前往后保证i min时取到最大的a max a[i]=max(a[i],maxn); maxn=max(a[i],maxn); } for(int i=1;i<=n;++i) scanf("%d",&b[i]); sort(b+1,b+n+1); long long ans=0; int j=1; maxn=-mod; for(int i=n+1;i<=2*n;++i) { a[i]=max(maxn,a[b[j]]); ans+=a[i]; ans%=mod; a[i]-=i;//新取的元素用过后当成已知的元素 maxn=max(maxn,a[i]);//新取元素用过后当成已知的元素一起更新最大值 j++; } printf("%lld\n",ans); } return 0;}
ps:
做题时理解错题意了+_+以为是取a
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