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  • Petr and a Combination Lock

    Petr has just bought a new car. He's just arrived at the most known Petersburg's petrol station to refuel it when he suddenly discovered that the petrol tank is secured with a combination lock! The lock has a scale of 360360 degrees and a pointer which initially points at zero:

    Petr called his car dealer, who instructed him to rotate the lock's wheel exactly nn times. The ii-th rotation should be aiai degrees, either clockwise or counterclockwise, and after all nn rotations the pointer should again point at zero.

    This confused Petr a little bit as he isn't sure which rotations should be done clockwise and which should be done counterclockwise. As there are many possible ways of rotating the lock, help him and find out whether there exists at least one, such that after all nn rotations the pointer will point at zero again.

    Input

    The first line contains one integer nn (1n151≤n≤15) — the number of rotations.

    Each of the following nn lines contains one integer aiai (1ai1801≤ai≤180) — the angle of the ii-th rotation in degrees.

    Output

    If it is possible to do all the rotations so that the pointer will point at zero after all of them are performed, print a single word "YES". Otherwise, print "NO". Petr will probably buy a new car in this case.

    You can print each letter in any case (upper or lower).

    Examples
    input
    Copy
    3
    10
    20
    30
    
    output
    Copy
    YES
    
    input
    Copy
    3
    10
    10
    10
    
    output
    Copy
    NO
    
    input
    Copy
    3
    120
    120
    120
    
    output
    Copy
    YES
    
    Note

    In the first example, we can achieve our goal by applying the first and the second rotation clockwise, and performing the third rotation counterclockwise.

    In the second example, it's impossible to perform the rotations in order to make the pointer point at zero in the end.

    In the third example, Petr can do all three rotations clockwise. In this case, the whole wheel will be rotated by 360360 degrees clockwise and the pointer will point at zero again.


    前 i 次旋转下,是否可以旋转到 j 度的位置,那么转移方程有:dp[i][j] = dp[ i - 1 ][ j - a[i] ] | dp[ i - 1 ][ j + a[i] ]

    #include <iostream>
    #include <vector>
    #include <algorithm>
    #include <string>
    #include <set>
    #include <queue>
    #include <map>
    #include <sstream>
    #include <cstdio>
    #include <cstring>
    #include <numeric>
    #include <cmath>
    #include<unordered_set>
    #define ll long long
    using namespace std;
    int dir[4][2] = { {1,0},{-1,0},{0,1},{0,-1} };
    
    int main()
    {
        int n;
        cin >> n;
        vector<int> a(n+1);
        for (int i = 1; i <= n; i++)
            cin >> a[i];
        vector<vector<bool>> dp(16, vector<bool>(360));
        dp[0][0] = true;
        for (int i = 1; i <= n; i++)
        {
            for (int j = 0; j < 360; j++)
            {
                if (dp[i - 1][(j - a[i] + 360) % 360])
                    dp[i][j] = true;
                if (dp[i - 1][(j + a[i] + 360) % 360])
                    dp[i][j] = true;
            }
        }
        cout << (dp[n][0] ? "YES" : "NO") << endl;
        //system("pause");
        return 0;
    }
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  • 原文地址:https://www.cnblogs.com/dealer/p/12297430.html
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