2016湖南省省赛G题

                                       G - Parenthesis

 

Bobo has a balanced parenthesis sequence P=p ₁ p ₂…p _n of length n and q questions.

The i-th question is whether P remains balanced after p _ai and p _bi  swapped. Note that questions are individual so that they have no affect on others.

Parenthesis sequence S is balanced if and only if:

1.  S is empty;

2.  or there exists balanced parenthesis sequence A,B such that S=AB;

3.  or there exists balanced parenthesis sequence S' such that S=(S').

Input

The input contains at most 30 sets. For each set:

The first line contains two integers n,q (2≤n≤10 ⁵,1≤q≤10 ⁵).

The second line contains n characters p ₁ p ₂…p _n.

The i-th of the last q lines contains 2 integers a _i,b _i (1≤a _i,b _i≤n,a _i≠b _i).

Output

For each question, output " Yes" if P remains balanced, or " No" otherwise.

Sample Input

4 2(())1 32 32 1()1 2

Sample Output

NoYesNo

题解：就是一个括号配对问题。

下面附上代码：

#include<stdio.h>#include<algorithm>#include<stack>using namespace std;char str[100005];int main(){    int n, m;    while(~scanf("%d%d", &n, &m))    {        scanf("%s", str+1);        int a, b;        for(int i = 1; i <= m; i++)        {            scanf("%d%d", &a, &b);            if(a>b) swap(a,b);            if(str[b]=='(' || str[a] == str[b])//这个地方不加前面的str[b]=='('，就会超时。            {                printf("Yes\n");                continue;            }            swap(str[a], str[b]);            int ans = 0;            for(int i = 1; i <= n; i++)            {                if(str[i] == '(') ans++;                else ans--;                if(ans < 0) { printf("No\n"); break;}            }            if(ans == 0) printf("Yes\n");            swap(str[a], str[b]);        }    }    return 0;}