Problem:
Score : 500 points

Problem Statement

You are given a string S consisting of 0 and 1.
Find the maximum integer K not greater than |S| such that we can turn all the characters of S into 0 by repeating the following operation some number of times.

Choose a contiguous segment [l,r] in S whose length is at least K (that is, r-l+1\geq K must be satisfied). For each integer i such that l\leq i\leq r, do the following: if S_i is 0, replace it with 1; if S_i is 1, replace it with 0.

Constraints

1\leq |S|\leq 10^5

S_i(1\leq i\leq N) is either 0 or 1.

Input

Input is given from Standard Input in the following format:

S

Output

Print the maximum integer K such that we can turn all the characters of S into 0 by repeating the operation some number of times.

Sample Input 1

010

Sample Output 1

2

We can turn all the characters of S into 0 by the following operations:

Perform the operation on the segment S[1,3] with length 3. S is now 101.

Perform the operation on the segment S[1,2] with length 2. S is now 011.

Perform the operation on the segment S[2,3] with length 2. S is now 000.

Sample Input 2

100000000

Sample Output 2

8

Sample Input 3

00001111

Sample Output 3

4

Solution in Rust (1.15.1) (judge verdict: Wrong Answer)

use std::cmp;

fn main() {
    let mut sc = Scanner::new();
    let s: Vec<char> = sc.read::<String>().chars().collect();
    let n = s.len();
    let mut cur = s[0];
    let mut count = 1;
    let mut segments = Vec::new();
    for i in 1..s.len() {
        if s[i] == cur {
            count += 1;
        } else {
            segments.push(count);
            cur = s[i];
            count = 1;
        }
    }
    segments.push(count);
    if segments.len() == 1 {
        println!("{}", s.len());
        return;
    }

    let mut max = 0;
    let mut prefix = 0;
    for i in 0..(segments.len() - 1) {
        let x = segments[i] + segments[i + 1];
        let suffix_space = n - segments[i];
        let prefix_space = prefix + segments[i];
        let mut min = cmp::min(suffix_space, prefix_space);
        min = cmp::min(min, x);
        max = cmp::max(max, min);
        prefix += segments[i];
    }

    prefix = 0;
    segments.reverse();
    for i in 0..(segments.len() - 1) {
        let x = segments[i] + segments[i + 1];
        let suffix_space = n - segments[i];
        let prefix_space = prefix + segments[i];
        let mut min = cmp::min(suffix_space, prefix_space);
        min = cmp::min(min, x);
        max = cmp::max(max, min);
        prefix += segments[i];
    }

    max = cmp::max(max, *segments.iter().max().unwrap());
    println!("{}", max);
}

struct Scanner {
    ptr: usize,
    length: usize,
    buf: Vec<u8>,
    small_cache: Vec<u8>,
}

impl Scanner {
    fn new() -> Scanner {
        Scanner { ptr: 0, length: 0, buf: vec![0; 1024], small_cache: vec![0; 1024] }
    }

    fn load(&mut self) {
        use std::io::Read;
        let mut s = std::io::stdin();
        self.length = s.read(&mut self.buf).unwrap();
    }

    fn byte(&mut self) -> u8 {
        if self.ptr >= self.length {
            self.ptr = 0;
            self.load();
            if self.length == 0 {
                self.buf[0] = b'\n';
                self.length = 1;
            }
        }

        self.ptr += 1;
        return self.buf[self.ptr - 1];
    }

    fn is_space(b: u8) -> bool { b == b'\n' || b == b'\r' || b == b'\t' || b == b' ' }

    fn read<T>(&mut self) -> T where T: std::str::FromStr, T::Err: std::fmt::Debug, {
        let mut b = self.byte();
        while Scanner::is_space(b) {
            b = self.byte();
        }

        for pos in 0..self.small_cache.len() {
            self.small_cache[pos] = b;
            b = self.byte();
            if Scanner::is_space(b) {
                return String::from_utf8_lossy(&self.small_cache[0..(pos + 1)]).parse().unwrap();
            }
        }

        let mut v = self.small_cache.clone();
        while !Scanner::is_space(b) {
            v.push(b);
            b = self.byte();
        }
        return String::from_utf8_lossy(&v).parse().unwrap();
    }
}