[HDOJ 5183] Negative and Positive (NP) 【Hash】

题目链接:HDOJ - 5183

 

题目分析

分两种情况,奇数位正偶数位负或者相反。

从1到n枚举,在Hash表中查询 Sum[i] - k ,然后将 Sum[i] 加入 Hash 表中。

BestCoder比赛的时候我写了 STL map, 然后TLE...

注意: Hash负数的时候 % 了一个质数,得到的是负数还要 + Mod !!

 

代码

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#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <queue>
#include <map>
#include <set>
#include <vector>
 
using namespace std;
 
#define Debug(x) cout << #x << " = " << x << endl
 
typedef long long LL;
typedef double DB;
 
inline int gmax(int a, int b) {return a > b ? a : b;}
inline int gmin(int a, int b) {return a < b ? a : b;}
 
inline void Read(int &Num)
{
    char c = getchar();
    bool Neg = false;
    while (c < '0' || c > '9')
    {
        if (c == '-') Neg = true;
        c = getchar();
    }
    Num = c - '0'; c = getchar();
    while (c >= '0' && c <= '9')
    {
        Num = Num * 10 + c - '0';
        c = getchar();
    }
    if (Neg) Num = -Num;
}
 
const int MaxN = 1000000 + 5, Mod = 1000007;
 
int T, n, k;
int A[MaxN];
 
struct HashNode
{
    int x;
    HashNode *Next;
} HA[MaxN], *P = HA, *Hash[2][Mod + 5];
 
bool Find(int f, LL Num)
{
    int HN = ((Num % Mod) + Mod) % Mod;
    for (HashNode *j = Hash[f][HN]; j; j = j -> Next)
        if (j -> x == Num) return true;
    return false;
}
 
void Insert(int f, LL Num)
{
    int HN = ((Num % Mod) + Mod) % Mod;
    ++P; P -> x = Num;
    P -> Next = Hash[f][HN]; Hash[f][HN] = P;
}
 
int main()
{  
    scanf("%d", &T);
    for (int Case = 1; Case <= T; ++Case)
    {
        memset(Hash, 0, sizeof(Hash));
        P = HA;
        scanf("%d%d", &n, &k);
        for (int i = 1; i <= n; ++i) Read(A[i]);
        int Temp;
        LL Sum0, Sum1;
        Sum0 = Sum1 = 0;
        Insert(1, 0);
        bool Flag = false;
        for (int i = 1; i <= n; ++i)
        {
            if (i & 1) Temp = -A[i];
            else Temp = A[i];
            Sum0 = Sum0 + (LL)Temp;
            Sum1 = Sum1 - (LL)Temp;
            if (Find(0, Sum0 - (LL)k) || Find(1, Sum1 - (LL)k))
            {
                Flag = true;
                break;
            }
            if (i & 1) Insert(0, Sum0);
            if ((i & 1) == 0) Insert(1, Sum1);
        }
        if (Flag) printf("Case #%d: Yes.\n", Case);
        else printf("Case #%d: No.\n", Case);
    }
    return 0;
}

  

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