代码

#include "router.h"

int n_entries;
unsigned one_bit_prefix[33], addr_mask[33];
RoutingTableEntry *routing_table;

void init(int n, int q, const RoutingTableEntry *a) {
    n_entries = n;
    routing_table = (RoutingTableEntry*) a;
    for (unsigned i = 1; i <= 32; ++ i)
        one_bit_prefix[i] = one_bit_prefix[i - 1] | (1ul << (32ul - i));
    for (int i = 0; i < n_entries; ++ i)
        routing_table[i].addr &= one_bit_prefix[routing_table[i].len];
}

unsigned query(unsigned addr) {
    for (int i = 0; i <= 32; ++ i)
        addr_mask[i] = addr & one_bit_prefix[i];
    int max_length = -1;
    unsigned nexthop;
    for (int i = 0; i < n_entries; ++ i) {
        if (addr_mask[routing_table[i].len] == routing_table[i].addr && routing_table[i].len > max_length) {
            max_length = routing_table[i].len;
            nexthop = routing_table[i].nexthop;
        }
    }
    if (max_length == -1)
	    return 0;
    return nexthop;
}

评测结果