T710668 C. 孤独的数字三 [Hello World 2026 蓝桥杯选拔赛]

#include <stdio.h>

#define maxn 100100
int n, ans, mx2;
int num[maxn], mx1[3] = {0};

int max(int a, int b) {
    return a > b ? a : b;
}

void add(int x) {
    int minIdx = 0;
    int i;
    for (i = 0; i < 3; ++i) {
        if (mx1[i] < mx1[minIdx]) {
            minIdx = i;
        }
    }
    if (x > mx1[minIdx]) {
        mx1[minIdx] = x;
    }
}

int main() {
    scanf("%d", &n);
    ans = 0;
    mx2 = 0;
    int i;
    for (i = 1; i <= n; ++i) {
        scanf("%d", &num[i]);
        if (num[i] % 3 == 2) {
            mx2 = max(mx2, num[i]);
        }
        if (num[i] % 3 == 1) {
            add(num[i]);
        }
    }
    if (mx2 != 0 && mx1[0] != 0) {
        ans = max(ans, mx2 + max(max(mx1[0], mx1[1]), mx1[2]));
    }
    if (mx1[2] != 0) {
        ans = max(ans, mx1[0] + mx1[1] + mx1[2]);
    }
    if (ans == 0) {
        printf("impossible\n");
    } else {
        printf("%d\n", ans);
    }

    return 0;
}