Problem:
MathJax.Hub.Config({ tex2jax: { inlineMath: [["$","$"], ["\\(","\\)"]], processEscapes: true }});

Maximum Profit

You can obtain profits from foreign exchange margin transactions. For example, if you buy 1000 dollar at a rate of 100 yen per dollar, and sell them at a rate of 108 yen per dollar, you can obtain (108 - 100) × 1000 = 8000 yen.

Write a program which reads values of a currency $R_t$ at a certain time $t$ ($t = 0, 1, 2, ... n-1$), and reports the maximum value of $R_j - R_i$ where $j > i$ .

Input

The first line contains an integer $n$. In the following $n$ lines, $R_t$ ($t = 0, 1, 2, ... n-1$) are given in order.

Output

Print the maximum value in a line.

Constraints

$2 \leq n \leq 200,000$

$1 \leq R_t \leq 10^9$

Sample Input 1

6
5
3
1
3
4
3

Sample Output 1

3

Sample Input 2

3
4
3
2

Sample Output 2

-1

Solution in Rust (judge verdict: Accepted)

use std::env;
use std::io;
use std::io::prelude::*;

//===================================================
// MACROs need to be defined above the use place ... ?
macro_rules! dprintln {
    ($($x:expr),*) => {{
        if $crate::is_debug_mode() {
            let f = || {println!( $($x),*)};
            f()
        }
    }}
}

//===================================================

fn main() {
    // Initialize
    set_debug_mode(false);
    for arg in env::args() {
        if arg == "--debug" {
            set_debug_mode(true);
        }
    }
    dprintln!("[DebugMode] {}", "On");

    // Execute
    dprintln!("=================");
    dprintln!("= READ INPUT     ");
    let stdin = io::stdin();
    let input = Input::new(stdin.lock());
    dprintln!("[Input] \n{:?}", input);
    dprintln!("=================");
    dprintln!("= INTERPRET INPUT");
    let q = input.into_quiz();
    dprintln!("[Quiz] \n{:?}", q);
    dprintln!("=================");
    dprintln!("= SOLVE QUIZE    ");
    let a = q.solve();
    dprintln!("[Answer] \n{:?}", a);
    dprintln!("=================");
    dprintln!("= PRINT ANSWER   ");
    a.print();
    dprintln!("=================");
}

#[derive(Debug)]
struct Quiz {
    n: u32,      // 2 <= n <= 200,000
    v: Vec<i32>, // 1 <= v[i] <= 10^9, length=n
}

#[derive(Debug)]
struct Answer {
    sa: i32,
}

impl Input {
    fn into_quiz(mut self) -> Quiz {
        let n: u32 = self.parse_next().unwrap();
        let v: Vec<i32> = self.parse_next_vec(n as usize).unwrap();
        Quiz { n, v }
    }
}

impl Quiz {
    fn solve(self) -> Answer {
        let mut i = 0usize;
        let mut j = 1usize;
        let mut min = self.v[i];
        let mut max_earn = self.v[j] - min;

        let length = self.n as usize;

        dprintln!("first:");
        dprintln!(" v[{}]:{} - v[{}]:{} = {}]", j, self.v[j], i, self.v[i], max_earn);
        for k in 1usize..length {
            dprintln!("k={}:  v[k]={}", k, self.v[k]);

            if max_earn < self.v[k] - min {
                dprintln!(" --- update max earn");
                j = k;
                max_earn = self.v[j] - min; 
            }

            if min > self.v[k] {
                dprintln!(" --- update min");
                i = k;
                min = self.v[i];
            }

            dprintln!(" v[{}]:{} - v[{}]:{} = {}]", j, self.v[j], i, self.v[i], max_earn);
        }

        Answer{ sa: max_earn }
    }
}

impl Answer {
    fn print(self) {
        println!("{}", self.sa);
    }
}

// =====================================================
// =
// =====================================================

//==================================================
// Stdin Reader
#[derive(Debug)]
pub enum Token {
    Word(String),
    LineBreak,
}

impl Token {
    pub fn is_word(&self) -> bool {
        match *self {
            Token::Word(ref _x) => true,
            _ => false,
        }
    }
}

#[derive(Debug)]
pub struct Input {
    tokens: Vec<Token>,
}

impl Input {
    pub fn new<T: BufRead>(input: T) -> Self {
        let lines = input.lines();
        let words = lines.flat_map(|l| tokenaize(l.unwrap()));
        let mut words = words.collect::<Vec<_>>();

        words.reverse();

        Input { tokens: words }
    }

    pub fn read_next_word(&mut self) -> Option<Token> {
        loop {
            match self.tokens.pop() {
                Some(Token::LineBreak) => (),
                x => return x,
            }
        }
    }

    pub fn parse_next<T>(&mut self) -> Option<T>
    where
        T: std::str::FromStr,
    {
        if let Some(Token::Word(str)) = self.read_next_word() {
            match str.parse() {
                Ok(x) => Some(x),
                _ => None,
            }
        } else {
            None
        }
    }

    pub fn parse_next_vec<T>(&mut self, size: usize) -> Option<Vec<T>>
    where
        T: std::str::FromStr,
    {
        let mut v = Vec::new();

        for _i in 0..size {
            if let Some(t) = self.parse_next() {
                v.push(t);
            } else {
                return None;
            }
        }

        Some(v)
    }

    pub fn parse_next_vec2<T>(&mut self, size2: usize, size1: usize) -> Option<Vec<Vec<T>>>
    where
        T: std::str::FromStr,
    {
        let mut v = Vec::new();

        for _i in 0..size2 {
            if let Some(t) = self.parse_next_vec(size1) {
                v.push(t);
            } else {
                return None;
            }
        }

        Some(v)
    }
}

fn tokenaize(str: String) -> Vec<Token> {
    let mut v = Vec::new();

    for w in str.split_whitespace() {
        v.push(Token::Word(w.to_string()));
    }
    v.push(Token::LineBreak);
    v
}

//==================================================
// Utility Functions
pub fn concat_vec_to_string<T>(v: &Vec<T>) -> String
where
    T: std::fmt::Display,
{
    let mut string = String::new();

    if let Some((h, t)) = v.split_first() {
        string = h.to_string();

        for obj in t {
            string = format!("{} {}", string, obj);
        }
    }

    return string;
}

//==================================================
// Debug Switch
static mut S_DEBUG_MODE: bool = false;
fn is_debug_mode() -> bool {
    unsafe { S_DEBUG_MODE }
}

fn set_debug_mode(mode: bool) {
    unsafe {
        S_DEBUG_MODE = mode;
    }
}