codeforces 134Cswap

C. Swaps

time limit per test

2 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

There are n players sitting at a round table. All of them have s cards of n colors in total. Besides, initially the first person had cards of only the first color, the second one had cards of only the second color and so on. They can swap the cards by the following rules:

• as the players swap, a player can give a card of his color only;
• a player can't accept a card of a color he already has (particularly, he can't take cards of his color, no matter whether he has given out all of them or not);
• during one swap a pair of people swaps cards (each person gives one card and takes one card).

The aim of all n people is as follows: each of them should give out all the cards he had initially (that is, all cards of his color). Your task is to denote whether such sequence of swaps is possible. If the answer is positive, you should list all the swaps.

Input

The first line contains integers n (1 ≤ n ≤ 200000) and s (1 ≤ s ≤ 200000). The second line contains nnumbers, the i-th number stands for how many cards the i-th player has by the moment the game starts. It is possible that a player has no cards initially.

Output

On the first line print "No" if such sequence of swaps is impossible. Otherwise, print "Yes". If the answer is positive, next print number k — the number of the swaps. Then on k lines describe the swaps by pairs of indices of the swapping players. Print the swaps and the numbers of the swaps in any order.

Sample test(s)

input

4 82 2 2 2

output

Yes44 34 21 31 2

input

6 121 1 2 2 3 3

output

Yes66 56 46 35 45 32 1

input

5 50 0 0 0 5

output

No

通过这题收获很大！。  学习到了优先队列和pair调用的简单用法.//make_pair()  ,priority_queue();......

这题就是优先队列+bfs...一开始思考的时候完全不知道怎么做。

下面是AC代码：

#include<iostream>#include<queue>using namespace std;#define N 200009              //怎么老喜欢给它加分号结尾呢typedef pair <int ,int > pai;pai ans[N];int main(){int n,s,i,a;int num=0;cin>>n>>s;priority_queue<pai>q,t;for(i=1;i<=n;i++){scanf("%d",&a);q.push(make_pair(a,i));            //构成一对}while(!q.empty()){pai p=q.top();  q.pop();           //和栈一样是top，而不是front‘while(p.first!=0){if(q.empty()){puts("No");return 0;}pai v=q.top(); q.pop();ans[++num]=make_pair(p.second,v.second);p.first--;v.first--;if(v.first)t.push(v);}   while(!t.empty())         {            q.push(t.top());            t.pop();        }}puts("Yes");printf("%d\n",num);for(i=1;i<=num;i++)printf("%d %d\n",ans[i].first,ans[i].second);return 0;}