codeforces D. Queue 找规律+递推

题目链接：

http://codeforces.com/problemset/problem/353/D?mobile=true

H. Queue

time limit per test 1 second
memory limit per test 256 megabytes
#### 问题描述
> There are n schoolchildren, boys and girls, lined up in the school canteen in front of the bun stall. The buns aren't ready yet and the line is undergoing some changes.
>
> Each second all boys that stand right in front of girls, simultaneously swap places with the girls (so that the girls could go closer to the beginning of the line). In other words, if at some time the i-th position has a boy and the (i + 1)-th position has a girl, then in a second, the i-th position will have a girl and the (i + 1)-th one will have a boy.
>
> Let's take an example of a line of four people: a boy, a boy, a girl, a girl (from the beginning to the end of the line). Next second the line will look like that: a boy, a girl, a boy, a girl. Next second it will be a girl, a boy, a girl, a boy. Next second it will be a girl, a girl, a boy, a boy. The line won't change any more.
>
> Your task is: given the arrangement of the children in the line to determine the time needed to move all girls in front of boys (in the example above it takes 3 seconds). Baking buns takes a lot of time, so no one leaves the line until the line stops changing.
#### 输入
> The first line contains a sequence of letters without spaces s1s2... sn (1 ≤ n ≤ 106), consisting of capital English letters M and F. If letter si equals M, that means that initially, the line had a boy on the i-th position. If letter si equals F, then initially the line had a girl on the i-th position.
#### 输出
> Print a single integer — the number of seconds needed to move all the girls in the line in front of the boys. If the line has only boys or only girls, print 0.
#### 样例
> **sample input**
> MMFF
>
> **sample output**
> 3

题意

题解

代码

#include<iostream>

#include<cstdio>

#include<cstring>

#include<algorithm>

#include<queue>

#include<map>

#define lson (o<<1)

#define rson ((o<<1)|1)

#define M (l+(r-l)/2)

using namespace std;

const int maxn = 1e6 + 10;

char str[maxn];

int sumv[maxn];

int main() {

	int a = 0, b = 0;

	scanf("%s", str);

	int n = strlen(str);

	int p = 0,cntm=0,ans=0;

	while (p < n&&str[p] == 'F') p++;

	for (int i = p; i < n; i++) {

		if (str[i] == 'M') {

			cntm++;

		}

		else {

			ans = max(ans + 1, cntm);

		}

	}

	printf("%d\n", ans);

	return 0;

}

Notes