題目大意:給定括號總數n,再給出每組括號的左右半邊的下標相差範圍L, R,求滿足條件的括號序列,若不存在則輸出IMPOSSIBLE
pos[i]:第i個括號的左半邊的位置
len:當前字符串長度
括號匹配成功的條件:pos[i]+L[i]<=len+1<=pos[i]+R[i];
#include <cstdio>
#include <stack>
using namespace std;
const int N = 610;
char ans[2*N];
int len;
int L[N], R[N], pos[N];
int main()
{
int n;
scanf("%d", &n);
len = 0;
stack <int> s;
for(int i = 1; i <= n; ++i)
{
scanf("%d %d", &L[i], &R[i]);
s.push(i);
ans[++len] = '(';
pos[i] = len;//棧頂元素的位置
while(!s.empty() && pos[s.top()]+L[s.top()]<=len+1)
{
if(pos[s.top()]+R[s.top()] < len+1)
return 0*printf("IMPOSSIBLE\n");
ans[++len] = ')';
s.pop();
}
}
ans[++len] = '\0';
if(s.empty()) puts(ans+1);
else printf("IMPOSSIBLE\n");
return 0;
}