HDU 5183 Negative and Positive (NP) (handwritten hash)

Topic links: HDU 5183

Problem Description

When given an array \((a_0,a_1,a_2,⋯a_{n−1})\) and an integer \(K\), you are expected to judge whether there is a pair \((i,j)(0≤i≤j<n)\) which makes that \(NP−sum(i,j)\) equals to \(K\) true. Here \(NP−sum(i,j)=a_i−a_{i+1}+a_{i+2}+⋯+(−1)^{j−i}a_j\)

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 \(2∗T\) 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 \((a_0,a_1,a_2,⋯a_{n−1})\) separated by exact one space.

[Technical Specification]

All input items are integers.

\(0<T≤25,1≤n≤1000000,−1000000000≤a_i≤1000000000,−1000000000≤K≤1000000000\)

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 \(PN−sum(i,j)\) equals to \(K\).

See the sample for more details.

Sample Input

Sample Output

Case #1: Yes.
Case #2: No.

Hint

If input is huge, fast IO method is recommended.

Source

BestCoder Round #32

Solution

The meaning of problems

A given length of \ (n-\) arrays, and asked whether there is some interval equal to its subtraction interleaved \ (K \) .

Thinking

Seeking a prefix to the array and then hash on the line.

But a different set of questions that could not pass.

So to handwritten hash.

Of course, you can also unordered_set too.

Code

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int maxn = 1e6 + 7;

struct HashMap {
    int head[maxn], next[maxn];
    ll num[maxn];
    int tot;
    inline void init() {
        tot = 0;
        memset(head, -1, sizeof(head));
    }
    inline void insert(ll val) {
        int h = abs(val) % maxn;
        num[tot] = val, next[tot] = head[h], head[h] = tot++;
    }
    inline bool find(ll val) {
        int h = abs(val) % maxn;
        for(int i = head[h]; ~i; i = next[i]) {
            if(num[i] == val) {
                return true;
            }
        }
        return false;
    }
} hashmap;

ll arr[maxn], sum[maxn];

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int T;
    cin >> T;
    int kase = 0;
    while(T--) {
        hashmap.init();
        ll n, k;
        cin >> n >> k;
        for(int i = 1; i <= n; ++i) {
            cin >> arr[i];
            sum[i] = sum[i - 1] + (i & 1? arr[i]: -arr[i]);
        }
        int flag = 0;
        for(int i = n; i; --i) {
            hashmap.insert(sum[i]);
            if(i & 1) {
                if(hashmap.find(sum[i - 1] + k)) {
                    flag = 1;
                    break;
                }
            } else {
                if(hashmap.find(sum[i - 1] - k)) {
                    flag = 1;
                    break;
                }
            }
        }
        cout << "Case #" << ++kase << ": " << (flag? "Yes." : "No.") << endl;
    }
    return 0;
}