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  • bestcoder#32 1002 哈希+后缀数组

    bestcoder#32 1002 哈希+后缀数组

    Negative and Positive (NP)


    Time Limit: 3000/1500 MS (Java/Others)    Memory Limit: 65536/65536 K (Java/Others)
    Total Submission(s): 1161    Accepted Submission(s): 59


    Problem Description
    When given an array (a0,a1,a2,an1) and an integer K, you are expected to judge whether there is a pair (i,j)(0ij<n) which makes that NPsum(i,j) equals to K true. Here NPsum(i,j)=aiai+1+ai+2++(1)jiaj
     
    Input
    Multi test cases. In the first line of the input file there is an integer T indicates the number of test cases.
    In the next 2T lines, it will list the data for each test case.
    Each case occupies two lines, the first line contain two integers n and K which are mentioned above.
    The second line contain (a0,a1,a2,an1)separated by exact one space.
    [Technical Specification]
    All input items are integers.
    0<T25,1n1000000,1000000000ai1000000000,1000000000K1000000000
     
    Output
    For each case,the output should occupies exactly one line. The output format is Case #id: ans, here id is the data number starting from 1; ans is “Yes.” or “No.” (without quote) according to whether you can find (i,j) which makes PNsum(i,j) equals to K.
    See the sample for more details.
     
    Sample Input
    2
    1 1
    1
    2 1
    -1 0
     
    Sample Output
    Case #1: Yes.
    Case #2: No.
     
    题意:查找是否存在sum(i,j)==K
    思路:构造前缀和d[],对sum(i,j)=d[j]-d[i-1],从n到1遍历i-1,插入d[i-1],从哈希表中查找是否存在d[i-1]+K;
    注意这里不从1到n遍历j是因为项的正负是由i-1决定,所以比较方便;当然从n开始遍历j更容易理解,但不好处理正负号
    题目还卡了STL的set,更坑的是还卡了scanf,我也因此学会了手写hash和读入外挂,很好的一道题
    #include<iostream>
    #include<cstdio>
    #include<cstring>
    #include<cstdlib>
    #include<ctype.h>
    #include<algorithm>
    #include<cmath>
    #include<set>
    
    using namespace std;
    
    const int maxn=1000100;
    const int HM=100100;
    int n,K;
    int a[maxn];
    long long d[maxn];
    
    struct Hash
    {
        long long date;
        Hash *next;
    };Hash h[HM];
    
    void insert(long long date,Hash *h)
    {
        int t=abs(date)%HM;
        Hash *pre=&h[t],*p=pre->next;
        while(p!=NULL){
            if(p->date=date) return;
            pre=p;
            p=p->next;
        }
        p=(Hash*)malloc(sizeof(Hash));
        p->date=date;p->next=NULL;
        pre->next=p;
    }
    
    bool find(long long date,Hash *h)
    {
        int t=abs(date)%HM;
        Hash *pre=&h[t],*p=pre->next;
        while(p!=NULL){
            if(p->date==date) return true;
            pre=p;
            p=p->next;
        }
        return false;
    }
    
    inline int read()
    {
        char c=getchar();
        while(c!='-'&&!isdigit(c)) c=getchar();
        int f=0,tag=1;
        if(c=='-'){
            tag=-1;
            f=getchar()-'0';
        }
        else f=c-'0';
        while(isdigit(c=getchar())) f=f*10+c-'0';
        return f*tag;
    }
    
    int main()
    {
        int T=read();
        int tag=1;
        while(T--){
            n=read();K=read();
            d[0]=0;
            for(int i=1;i<=n;i++){
                a[i]=read();
                if(i&1) d[i]=d[i-1]+a[i];
                else d[i]=d[i-1]-a[i];
            }
            for(int i=0;i<HM;i++) h[i].next=NULL;
            bool flag=0;
            for(int i=n;i>=0;i--){
                insert(d[i],h);
                if(i&1){
                    if(find(d[i]-K,h)) flag=1;
                }
                else if(find(d[i]+K,h)) flag=1;
                if(flag) break;
            }
            printf("Case #%d: ",tag++);
            if(flag) printf("Yes.
    ");
            else printf("No.
    ");
        }
        return 0;
    }
    bestcoder#32_1002
    没有AC不了的题,只有不努力的ACMER!
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  • 原文地址:https://www.cnblogs.com/--560/p/4332548.html
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