Codeforces 501C - Misha and Forest (机智)

题意

给出每个点的度数和和这个点连接的点的异或和，输出图的每条边。

思路

看了squee_spoon的题解。

这题的突破口在于叶子。因为叶子的sum就是点的编号。

所以在读取输入的时候把num为1的点都加入到队列，然后取出来，之后就能得到一条边。以此类推

代码

  
  
  
  

   
   
   
   
#include <cstdio>
   
   
   
   
#include <stack>
   
   
   
   
#include <list>
   
   
   
   
#include <set>
   
   
   
   
#include <iostream>
   
   
   
   
#include <string>
   
   
   
   
#include <vector>
   
   
   
   
#include <queue>
   
   
   
   
#include <functional>
   
   
   
   
#include <cstring>
   
   
   
   
#include <algorithm>
   
   
   
   
#include <cctype>
   
   
   
   
#include <string>
   
   
   
   
#include <map>
   
   
   
   
#include <cmath>
   
   
   
   
using namespace std;
   
   
   
   
#define LL long long
   
   
   
   
#define ULL unsigned long long
   
   
   
   
#define SZ(x) (int)x.size()
   
   
   
   
#define Lowbit(x) ((x) & (-x))
   
   
   
   
#define MP(a, b) make_pair(a, b)
   
   
   
   
#define MS(arr, num) memset(arr, num, sizeof(arr))
   
   
   
   
#define PB push_back
   
   
   
   
#define F first
   
   
   
   
#define S second
   
   
   
   
#define ROP freopen("input.txt", "r", stdin);
   
   
   
   
#define MID(a, b) (a + ((b - a) >> 1))
   
   
   
   
#define LC rt << 1, l, mid
   
   
   
   
#define RC rt << 1|1, mid + 1, r
   
   
   
   
#define LRT rt << 1
   
   
   
   
#define RRT rt << 1|1
   
   
   
   
#define BitCount(x) __builtin_popcount(x)
   
   
   
   
#define BitCountll(x) __builtin_popcountll(x)
   
   
   
   
#define LeftPos(x) 32 - __builtin_clz(x) - 1
   
   
   
   
#define LeftPosll(x) 64 - __builtin_clzll(x) - 1
   
   
   
   
const double PI = acos(-1.0);
   
   
   
   
const int INF = 0x3f3f3f3f;
   
   
   
   
const double eps = 1e-8;
   
   
   
   
const int MAXN = 100000 + 10;
   
   
   
   
const int MOD = 1000007;
   
   
   
   
const int dir[][2] = { {-1, 0}, {1, 0}, {0, -1}, {0, 1} };
   
   
   
   
typedef pair<int, int> pii;
   
   
   
   
typedef vector<int>::iterator viti;
   
   
   
   
typedef vector<pii>::iterator vitii;
   
   
   
   

   
   
   
   
struct POINT
   
   
   
   
{
   
   
   
   
 int num, sum;
   
   
   
   
}arr[MAXN];
   
   
   
   

   
   
   
   
queue<int> Q;
   
   
   
   

   
   
   
   
int main()
   
   
   
   
{
   
   
   
   
 //ROP;
   
   
   
   
 int n, i, j;
   
   
   
   
 scanf("%d", &n);
   
   
   
   
 int ans = 0;
   
   
   
   
 for (i = 0; i < n; i++)
   
   
   
   
 {
   
   
   
   
 scanf("%d%d", &arr[i].num, &arr[i].sum);
   
   
   
   
 ans += arr[i].num;
   
   
   
   
 if (arr[i].num == 1) Q.push(i);
   
   
   
   
 }
   
   
   
   
 printf("%d\n", (ans>>1));
   
   
   
   
 while (!Q.empty())
   
   
   
   
 {
   
   
   
   
 int leaf = Q.front(); Q.pop();
   
   
   
   
 if (arr[leaf].num == 0) continue;
   
   
   
   
 arr[leaf].num--;
   
   
   
   
 int u = arr[leaf].sum;
   
   
   
   
 arr[u].num--;
   
   
   
   
 arr[u].sum ^= leaf;
   
   
   
   
 if (arr[u].num == 1) Q.push(u);
   
   
   
   
 printf("%d %d\n", leaf, u);
   
   
   
   
 }
   
   
   
   
 return 0;
   
   
   
   
}