codeforces 338e

本文介绍了一种使用线段树解决特定匹配问题的方法。该问题要求找出满足一定条件的所有子序列,通过贪心策略匹配两个数组中的元素,并确保它们的和大于等于一个特定值。文章详细解释了算法思路,并提供了完整的实现代码。

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题意:根据伪代码 求出答案

思路:其实他要我们求的是一个符合他条件 a[] 的连续的子串有多少个 这个字串必须满足一个条件 就是经过和b[]任意的匹配后 每一对数之和需要大于等于 一个特定的值  那么 最优的方案就是贪心  子串最大的 和  最小的b[]的匹配 第二大和第二小的 。。。。 如此匹配 虽然源代码得到的最后匹配不是这个 但是如果不满足这个方案 就肯定无解

对于每个a[] 我们可以从b[]中知道在他可以匹配的最小b[]是多少 记位置为x 那么b[]  x 到 m 小的值都可以匹配 于是用线段树来进行区间更新


ps:想到用区间更新了 但是以为自己想的那样会超时  结果就没写出来  看来别人代码才知道  底子不扎实 自己骗自己 


#include<cstring>
#include<cstdlib>
#include<iostream>
#include<stdio.h>
#include<cmath>
#include<algorithm>
#include<queue>
#include<vector>
using namespace std;
#define N 150010
#define MOD 1000000009
#define LL long long

int a[N];
int b[N];
int c[N*4];
int p[N*4];
int q[N*4];

int n,m,k;

void update(int tt)
{
    c[tt*2]+=p[tt];c[tt*2+1]+=p[tt];
    p[tt*2]+=p[tt];p[tt*2+1]+=p[tt];
    p[tt]=0;
}

void change(int l,int r,int tt,int x,int y,int k)
{
    if(l==x&&r==y)
    {
        c[tt]+=k;
        p[tt]+=k;
        return ;
    }
    update(tt);
    int mid=(l+r)/2;
    if(x>mid)change(mid+1,r,tt*2+1,x,y,k);
    else if(y<=mid)change(l,mid,tt*2,x,y,k);
    else
    {
        change(mid+1,r,tt*2+1,mid+1,y,k);
        change(l,mid,tt*2,x,mid,k);
    }
    c[tt]=min(c[tt*2],c[tt*2+1]);
}

int fd(int x)
{
    int l=1,r=m,ret=m+1;
    while(l<=r)
    {
        int mid=(l+r)/2;
        if(x+a[mid]>=k)
        {
            ret=mid;
            r=mid-1;
        }
        else
        {
            l=mid+1;
        }
    }
    return ret;
}

int main()
{
    scanf("%d%d%d",&n,&m,&k);
    for(int i=1;i<=m;i++)
    {
        scanf("%d",&a[i]);
    }
    sort(a+1,a+m+1);
    for(int i=1;i<=m;i++) change(1,m,1,i,i,-i);
    int ans=0;
    for(int i=1;i<=n;i++)
    {
        scanf("%d",&b[i]);
        q[i]=fd(b[i]);
        if(q[i]<=m)change(1,m,1,q[i],m,1);
        if(i>m&&q[i-m]<=m)change(1,m,1,q[i-m],m,-1);
        ans+=c[1]>=0;
    }
    printf("%d\n",ans);
    return 0;
}


### Codeforces 887E Problem Solution and Discussion The problem **887E - The Great Game** on Codeforces involves a strategic game between two players who take turns to perform operations under specific rules. To tackle this challenge effectively, understanding both dynamic programming (DP) techniques and bitwise manipulation is crucial. #### Dynamic Programming Approach One effective method to approach this problem utilizes DP with memoization. By defining `dp[i][j]` as the optimal result when starting from state `(i,j)` where `i` represents current position and `j` indicates some status flag related to previous moves: ```cpp #include <bits/stdc++.h> using namespace std; const int MAXN = ...; // Define based on constraints int dp[MAXN][2]; // Function to calculate minimum steps using top-down DP int minSteps(int pos, bool prevMoveType) { if (pos >= N) return 0; if (dp[pos][prevMoveType] != -1) return dp[pos][prevMoveType]; int res = INT_MAX; // Try all possible next positions and update 'res' for (...) { /* Logic here */ } dp[pos][prevMoveType] = res; return res; } ``` This code snippet outlines how one might structure a solution involving recursive calls combined with caching results through an array named `dp`. #### Bitwise Operations Insight Another critical aspect lies within efficiently handling large integers via bitwise operators instead of arithmetic ones whenever applicable. This optimization can significantly reduce computation time especially given tight limits often found in competitive coding challenges like those hosted by platforms such as Codeforces[^1]. For detailed discussions about similar problems or more insights into solving strategies specifically tailored towards contest preparation, visiting forums dedicated to algorithmic contests would be beneficial. Websites associated directly with Codeforces offer rich resources including editorials written after each round which provide comprehensive explanations alongside alternative approaches taken by successful contestants during live events. --related questions-- 1. What are common pitfalls encountered while implementing dynamic programming solutions? 2. How does bit manipulation improve performance in algorithms dealing with integer values? 3. Can you recommend any online communities focused on discussing competitive programming tactics? 4. Are there particular patterns that frequently appear across different levels of difficulty within Codeforces contests?
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