2017秦皇岛ICPC

One-Dimensional Maze

BaoBao is trapped in a one-dimensional maze consisting of (n) grids arranged in a row! The grids are numbered from 1 to (n) from left to right, and the (i)-th grid is marked with a character (s_i), where (s_i) is either ‘L’ or ‘R’.

Starting from the (m)-th grid, BaoBao will repeatedly take the following steps until he escapes the maze:

If BaoBao is in the 1st grid or the (n)-th grid, then BaoBao is considered to arrive at the exit and thus can escape successfully.
Otherwise, let BaoBao be in the (t)-th grid. If (s_t = \text{‘L’}), BaoBao will move to the ((t-1))-th grid; If (s_t = \text{‘R’}), Baobao will move to the ((t+1))-th grid.
Before taking the above steps, BaoBao can change the characters in some grids to help himself escape. Concretely speaking, for the (i)-th grid, BaoBao can change (s_i) from ‘L’ to ‘R’, or from ‘R’ to ‘L’.

But changing characters in grids is a tiring job. Your task is to help BaoBao calculate the minimum number of grids he has to change to escape the maze.

Input
There are multiple test cases. The first line of the input contains an integer (T), indicating the number of test cases. For each test case:

The first line contains two integers (n) and (m) ((3 \le n \le 10^5), (1 < m < n)), indicating the number of grids in the maze, and the index of the starting grid.

The second line contains a string (s) ((|s| = n)) consisting of characters ‘L’ and ‘R’. The (i)-th character of (s) indicates the character in the (i)-th grid.

It is guaranteed that the sum of (n) over all test cases will not exceed (10^6).

Output
For each test case output one line containing one integer, indicating the minimum number of grids BaoBao has to change to escape the maze.

Sample Input
3
3 2
LRL
10 4
RRRRRRRLLR
7 4
RLLRLLR
Sample Output
0
2
1
Hint
For the first sample test case, BaoBao doesn’t have to change any character and can escape from the 3rd grid. So the answer is 0.

For the second sample test case, BaoBao can change (s_8) to ‘R’ and (s_9) to ‘R’ and escape from the 10th grid. So the answer is 2.

For the third sample test case, BaoBao can change (s_4) to ‘L’ and escape from the 1st grid. So the answer is 1.

题意： 给你一个字符串然后给你字符串的长度和一个index，字符串里的包括’L’或’R’代表当指针到这后需要向左移右移，如果可以走到两边的话算成功，问你需要最少的改变字符串里的元素使得最快成功

分析： 直接枚举就行，从中间向两边走，代码很简单，最签到题

#include<bits/stdc++.h>using namespace std;int main(){    ios_base::sync_with_stdio(0);    int T;cin>>T;    while(T--) {        int n,m;cin>>m>>n;        string s;cin>>s;        int ans,t1 = 0,t2 = 0;        int len  = s.size();        if(n == 1 || n == len) {            cout<<0<<endl;            continue;        }        for(int i = n-1;i < len-1;i++) {            if(s[i] == 'L') {                t1++;            }        }        for(int i = 1;i <= n-1;i++) {            if(s[i] == 'R') {                t2++;            }        }        ans = min(t2,t1);        cout<<ans<<endl;    }    return 0;}

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