Educational Codeforces Round 58 (Rated for Div. 2) B. Accordion

题解

题目大意 给你一个串让你删除一些字符找到最长的[?:] |可以有0个或多个

两侧向中心夹击 找到满足[:的最小的l和满足:]最大的r 最后统计中心有多少个|即可

AC代码

#include <stdio.h>
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

const int INF = 0x3f3f3f3f;
const int MAXN = 5e5 + 10;
char s[MAXN];

int main()
{
#ifdef LOCAL
	//freopen("C:/input.txt", "r", stdin);
#endif
	scanf("%s", s + 1);
	int n = strlen(s + 1);
	int l = 1, r = n, k = 0;
	while (l <= n && s[l] != '[') l++; //while确定位置
	while (l <= n && s[l] != ':') l++; //当找到[:会停下
	while (r >= 1 && s[r] != ']') r--;
	while (r >= 1 && s[r] != ':') r--;
	for (int i = l; i <= r; i++)
		if (s[i] == '|') k++;
	if (l >= r)
		cout << -1 << endl;
	else
		cout << 4 + k << endl;

	return 0;
}

从左向右一遍过的代码

#include <stdio.h>
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

const int INF = 0x3f3f3f3f;

int main()
{
#ifdef LOCAL
	freopen("C:/input.txt", "r", stdin);
#endif
	string s;
	cin >> s;
	int a = 0, b = -1, cnt = 0, ans = -1;
	for (int i = 0; s[i]; i++)
	{
		if (a == 0 && s[i] == '[')
			a = 1; //[
		else if (a == 1 && s[i] == ':')
			a = 2; //[:
		else if (a == 2) //左侧齐了
		{
			if (s[i] == '|')
				cnt++;
			if (s[i] == ':')
				b = 4 + cnt;
			if (s[i] == ']')
				ans = max(ans, b);
		}
	}
	cout << ans << endl;

	return 0;
}