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Underscores in Numeric Literals

긴 숫자를 선언할때 숫자사이에 언더스코어를 넣어서 가독성을 향상 시킬수 있다. 

숫자 구두점처럼 3자리마다 찍을 필요는 없고 숫자와 숫자 사이에서만 유효하다.

int price = 1000000;
int price =1_000_000;

 #78 Convert PascalCase string into snake_case

Complete the function/method so that it takes CamelCase string and returns the string in snake_case notation. Lowercase characters can be numbers. If method gets number, it should return string.

Examples:

//  returns test_controller

toUnderscore('TestController');

// returns movies_and_books

toUnderscore('MoviesAndBooks');

// returns app7_test

toUnderscore('App7Test');

// returns "1"

toUnderscore(1);

function toUnderscore(string) {
  return string.toString().replace(/\.?([A-Z])/g, function (x,y){return "_" + y.toLowerCase()}).replace(/^_/, "");
}

#77 Tortoise racing

Two tortoises named A and B must run a race. A starts with an average speed of 720 feet per hour. Young B knows she runs faster than A, and furthermore has not finished her cabbage.

When she starts, at last, she can see that A has a 70 feet lead but B's speed is 850 feet per hour. How long will it take B to catch A?

More generally: given two speeds v1 (A's speed, integer > 0) and v2 (B's speed, integer > 0) and a lead g (integer > 0) how long will it take B to catch A?

The result will be an array [hour, min, sec] which is the time needed in hours, minutes and seconds (round down to the nearest second) or a string in some languages.

If v1 >= v2 then return nil, nothing, null, None or {-1, -1, -1} for C++, C, Go, Nim, [] for Kotlin or "-1 -1 -1".

Examples:

(form of the result depends on the language)

race(720, 850, 70) => [0, 32, 18] or "0 32 18"

race(80, 91, 37)   => [3, 21, 49] or "3 21 49"

public class Tortoise {
    public static int[] race(int v1, int v2, int g) {

        if(v2 -v2 < 0)
        return null;

        double d = Double.valueOf(g)/(v2-v1);

        int hours = (int) d;
        int minutes = (int) (d * 60) % 60;
        int seconds = (int) (d * (60*60)) % 60;

        return new int [] {hours,minutes,seconds};

    }
}