QBXT 二月五号整理

给你一列数, 询问和最大的子串. N<=10^6

 // N <=10^6
 #include<cstdio>
 #include<iostream>
 using namespace std;
 int n,a[];
 int maxSubstr(){
     int sum=,minsum=,answer=;
     for(int i=;i<=n;++i){
         sum+=a[i];
         minsum=min(sum,minsum);
         answer=max(answer,sum-minsum);
     }
     printf("%d\n",answer);
 }
 int main()
 {
     scanf("%d",&n);
     for(int i=;i<=n;i++)
       scanf("%d",&a[i]);
     maxSubstr();
     return ;
 }

啊！！！好巧妙，幸亏当时记了笔记。。。

给你两列数 A; B, 定义一个子串 [l; r] 的权值为

∑r i=l Ai除以∑r i=l Bi 问权值最大的子串
n ≤ 10^5.

 /*二、给你两列数 A; B, 定义一个子串 [l; r] 的权值为
    ∑r i=l Ai
 k= ___________
    ∑r i=l Bi
 问权值最大的子串.*/
 const double inf = 1e32;
 int n, a[maxn], b[maxn];
 double c[maxn];
 double maxSubstr() {
     double sum = , minsum = inf, answer = -inf;
     for (int i = ; i <= n; ++ i) {
         sum += c[i];
         answer = max(answer, sum - minsum);
         minsum = min(sum, minsum);
     }
     return answer;
 }
 double erfen() {
     double l(-inf), r(inf);
     while (l + 1e- < r) {
         double mid = (l + r)/ ;
         for (int i = ; i <= n; ++ i) {
             c[i] = a[i] - mid * b[i];
         }
         if (maxSubstr() >= ) {
             l = mid;
         } else {
             r = mid - 1e-;
         }
     } //把分母乘过去二分答案
 }