代码

#include "router.h"
#include <stdint.h>
#include <stdlib.h>
#include <arpa/inet.h>

/*
  RoutingTable Entry 的定义如下：
  typedef struct {
    uint32_t addr; // 大端序，IPv4 地址
    uint32_t len; // 小端序，前缀长度
    uint32_t if_index; // 小端序，出端口编号
    uint32_t nexthop; // 大端序，下一跳的 IPv4 地址
  } RoutingTableEntry;

  约定 addr 和 nexthop 以 **大端序** 存储。
  这意味着 1.2.3.4 对应 0x04030201 而不是 0x01020304。
  保证 addr 仅最低 len 位可能出现非零。
  当 nexthop 为零时这是一条直连路由。
  你可以在全局变量中把路由表以一定的数据结构格式保存下来。
*/

void copyEntry(RoutingTableEntry * entry, RoutingTableEntry oldEntry) {
  entry -> addr = oldEntry.addr;
  entry -> len = oldEntry.len;
  entry -> if_index = oldEntry.if_index;
  entry -> nexthop = oldEntry.nexthop;
}

struct Node {
  RoutingTableEntry * entry = nullptr;
  Node * parent = nullptr;
  Node * lNode = nullptr, * rNode = nullptr;
};

class RoutingTrie {
  static Node * root;
public:
  static RoutingTableEntry * search(uint32_t addr) {
    addr = ntohl(addr);
    Node * node = root;
    RoutingTableEntry * entry = nullptr;
    for (int i = 0; i < 32; i ++) {
      int bit = addr >> 31;
      node = (bit == 0) ? node -> lNode : node -> rNode;
      if (node != nullptr) {
        entry = (node -> entry == nullptr) ? entry : node -> entry; 
      } else {
        break;
      }
      addr = addr << 1;
    }
    return entry;
  }

  static void insertNode(RoutingTableEntry entry) {
    uint32_t addr = ntohl(entry.addr);
    int len = entry.len;
    Node * node = root;
    for (int i = 0; i < len; i ++) {
      int bit = addr >> 31;
      if (bit == 0) {
        if (node -> lNode == nullptr) {
          node -> lNode = new Node;
          node -> lNode -> parent = node;
        }
        node = node -> lNode;
      } else {
        if (node -> rNode == nullptr) {
          node -> rNode = new Node;
          node -> rNode -> parent = node;
        }
        node = node -> rNode;
      }
      addr = addr << 1;
    }
    if (node -> entry != nullptr) {
      if (node -> entry -> addr == entry.addr) {
        copyEntry(node -> entry, entry);
      }
    } else {
      node -> entry = new RoutingTableEntry;
      copyEntry(node -> entry, entry);
    }
  }
  
  static void deleteNode(RoutingTableEntry entry) {
    uint32_t addr = ntohl(entry.addr), len = entry.len;
    Node * node = root;
    while (len != 0) {
      int bit = addr >> 31;
      node = (bit == 0) ? node -> lNode : node -> rNode;
      if (node != nullptr) {
        addr = addr << 1;
        len --;
      } else {
        break;
      }
    }
    if (len == 0) { //find node
      while (node != root) {
        if (node -> lNode == nullptr && node -> rNode == nullptr) {
          Node * deleteNode = node;
          node = node -> parent;
          delete deleteNode;
        } else {
          node -> entry = nullptr;
          break;
        }
      }
    }
  }

};

Node * RoutingTrie::root = new Node;

/**
 * @brief 插入/删除一条路由表表项
 * @param insert 如果要插入则为 true ，要删除则为 false
 * @param entry 要插入/删除的表项
 *
 * 插入时如果已经存在一条 addr 和 len 都相同的表项，则替换掉原有的。
 * 删除时按照 addr 和 len **精确** 匹配。
 */
void update(bool insert, RoutingTableEntry entry) {
  // TODO:
  if (insert) {
    RoutingTrie::insertNode(entry);
  } else {
    RoutingTrie::deleteNode(entry);
  }
}

/**
 * @brief 进行一次路由表的查询，按照最长前缀匹配原则
 * @param addr 需要查询的目标地址，大端序
 * @param nexthop 如果查询到目标，把表项的 nexthop 写入
 * @param if_index 如果查询到目标，把表项的 if_index 写入
 * @return 查到则返回 true ，没查到则返回 false
 */
bool prefix_query(uint32_t addr, uint32_t *nexthop, uint32_t *if_index) {
  // TODO:
  *nexthop = 0;
  *if_index = 0;
  RoutingTableEntry * entry = RoutingTrie::search(addr);
  if (entry != nullptr) {
    *nexthop = entry -> nexthop;
    *if_index = entry -> if_index;
    return true;
  }
  return false;
}


void init(int n, int q, const RoutingTableEntry *a) {
  for (int i = 0; i < n; i ++) {
    RoutingTrie::insertNode(a[i]);
  }
}

unsigned query(unsigned addr) {
  RoutingTableEntry * entry = RoutingTrie::search(addr);
  if (entry != nullptr) {
    return entry -> nexthop;
  }
  return 0;
}

评测结果