第一条题解，标准题解，不用函数

思路：用一个栈就行了，遇到左边push，遇到右边先判空，再pop，最后再判空

#include <bits/stdc++.h>
using namespace std;
string s;
stack <char> st;
int main() {
    cin >> s;
    for(int i = 0; i < s.length(); i++) {
        const char c = s[i];
        if(c == '(' || c == '[' || c == '{') {
            st.push(c);
        }
        else if(c == ')' || c == ']' || c == '}') {
            if(st.empty())  {
                cout << "false";
                return 0;
            }
            const char top = st.top();
            if(top == '(' && c == ')'
            || top == '[' && c == ']'
            || top == '{' && c == '}') {    //换行是为了好看
                st.pop();
            }
        }
    }
    if(!st.empty()) cout << "false";
    else cout << "true";
    return 0;
}

第一个沙发，发个火车头

#pragma G++ optimize(-01)
#pragma G++ optimize(-02)
#pragma G++ optimize(-03)
#pragma G++ optimize("Ofast")
#pragma G++ optimize("inline")
#pragma G++ optimize("-fgcse")
#pragma G++ optimize("-fgcse-lm")
#pragma G++ optimize("-fipa-sra")
#pragma G++ optimize("-ftree-pre")
#pragma G++ optimize("-ftree-vrp")
#pragma G++ optimize("-fpeephole2")
#pragma G++ optimize("-ffast-math")
#pragma G++ optimize("-fsched-spec")
#pragma G++ optimize("unroll-loops")
#pragma G++ optimize("-falign-jumps")
#pragma G++ optimize("-falign-loops")
#pragma G++ optimize("-falign-labels")
#pragma G++ optimize("-fdevirtualize")
#pragma G++ optimize("-fcaller-saves")
#pragma G++ optimize("-fcrossjumping")
#pragma G++ optimize("-fthread-jumps")
#pragma G++ optimize("-funroll-loops")
#pragma G++ optimize("-fwhole-program")
#pragma G++ optimize("-freorder-blocks")
#pragma G++ optimize("-fschedule-insns")
#pragma G++ optimize("inline-functions")
#pragma G++ optimize("-ftree-tail-merge")
#pragma G++ optimize("-fschedule-insns2")
#pragma G++ optimize("-fstrict-aliasing")
#pragma G++ optimize("-fstrict-overflow")
#pragma G++ optimize("-falign-functions")
#pragma G++ optimize("-fcse-skip-blocks")
#pragma G++ optimize("-fcse-follow-jumps")
#pragma G++ optimize("-fsched-interblock")
#pragma G++ optimize("-fpartial-inlining")
#pragma G++ optimize("no-stack-protector")
#pragma G++ optimize("-freorder-functions")
#pragma G++ optimize("-findirect-inlining")
#pragma G++ optimize("-frerun-cse-after-loop")
#pragma G++ optimize("inline-small-functions")
#pragma G++ optimize("-finline-small-functions")
#pragma G++ optimize("-ftree-switch-conversion")
#pragma G++ optimize("-foptimize-sibling-calls")
#pragma G++ optimize("-fexpensive-optimizations")
#pragma G++ optimize("-funsafe-loop-optimizations")
#pragma G++ optimize("inline-functions-called-once")
#pragma G++ optimize("-fdelete-null-pointer-checks") 
#include <bits/stdc++.h>
using namespace std;
int main() {
	return 0;
} 

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