Codeforces 484B Maximum Value (efficient + binary)

Codeforces 484B Maximum Value (efficient + binary)

Link: Codeforces 484B Maximum Value

Given a sequence, find the numbers of connected ai and aj, ai % aj should be as big as possible, and ai ≥ aj

Solution: similar to the prime number embedding method, each time we enumerate aj and then enumerate k, each time we use binary to find less than k? Aj and the largest ai, maintain the answer, and some pruning is added in the process.

#include 
  
   #include 
   
    #include using namespace std;const int maxn = 1e6+5;int N, a[maxn];int solve (int x) {    int ret = 0, p = x;    while (p < maxn) {        p += x;        int k = lower_bound(a, a + N, p) - a;        if (k == 0)    continue;        else k--;        if (a[k] <= x) continue;        ret = max(ret, a[k] % x);    }    return ret;}int main () {    scanf("%d", &N);    for (int i = 0; i < N; i++)        scanf("%d", &a[i]);    sort(a, a + N);    int ans = 0;    for (int i = N-1; i >= 0; i--) {        if (ans >= a[i] - 1)            break;        if (i < N - 1 && a[i] == a[i+1])            continue;        ans = max(ans, solve(a[i]));    }    printf("%d\n", ans);    return 0;}