【倍数问题——同余系】

题目

代码 

#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 10, M = 1e3 + 10;
int maxx[M][4];
void consider(int r, int x)
{if(x > maxx[r][1]){maxx[r][3] = maxx[r][2];maxx[r][2] = maxx[r][1];maxx[r][1] = x;}else if(x > maxx[r][2]){maxx[r][3] = maxx[r][2];maxx[r][2] = x;}else if(x > maxx[r][3])maxx[r][3] = x;
}
int cal(int i, int j, int t)
{if(i != j && i != t && j != t){return maxx[i][1] + maxx[j][1] + maxx[t][1];}else if(i == j && i == t && j == t){return maxx[i][1] + maxx[i][2] + maxx[i][3];}else{if(i == j){return maxx[i][1] + maxx[i][2] + maxx[t][1];}else if(i == t){return maxx[i][1] + maxx[i][2] + maxx[j][1];}else if(j == t){return maxx[j][1] + maxx[j][2] + maxx[i][1];}}
}
int main()
{int n, k;cin >> n >> k;for(int i = 0; i < k; i++){for(int j = 1; j <= 3; j++){maxx[i][j] = -1e8;}}for (int i = 1; i <= n; i++){int x;cin >> x;int r = x % k;consider(r, x);}int ans = 0;for (int i = 0; i < k; i++){for (int j = 0; j < k; j++){int t = (k - (i + j) % k) % k;ans = max(ans, cal(i, j, t));}}cout << ans;
}