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::vec::Vec;
use std::cmp::*;
fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>().split_whitespace().map(|e| e.parse().ok().unwrap()).collect()
}

fn main() {
    let s: Vec<char> = read::<String>().chars().collect();
    let n = s.len();
    let lst = split_same_element(&s);

    let mut n_one = 0;
    let mut n_zero = 0;
    for &(c, num) in &lst {
      if c == '0' {
        n_one += 1;
      } else {
        n_zero += 1;
      }
    }

    let mut len_one = 0;
    let mut tmp = 0;
    for i in 0..n_one {
      tmp += lst[i].1;
    }

    len_one = tmp;
    let mut tmp = 0;
    for j in ((lst.len() - n_one)..lst.len()) {
      tmp += lst[j].1;
    }
    len_one = max(tmp, len_one);

    let mut length = std::usize::MAX;
    for i in 0..lst.len()-1 {
      length = min(lst[i].1 + lst[i+1].1, length);
    }

    let ans = min(length, len_one);
    println!("{}", ans);
    //println!("length = {}", length);
    //println!("{}", len_one);
    //println!("n_one = {}, n_zero = {}", n_one, n_zero);
    //println!("{:?}", s);
    //println!("{:?}", lst);
}

fn split_same_element<T: Eq + Copy>(v: &Vec<T>) -> Vec<(T, usize)> {
  let mut res: Vec<(T, usize)> = Vec::new();
  if v.len() == 0 {
    return res;
  }

  let mut now: T = v[0];
  let mut count: usize = 0;
  for &e in v {
    if e == now {
      count += 1;
    }
    else {
      res.push((now, count));
      count = 1;
      now = e;
    }
  }
  res.push((now, count));

  res
}