Problems: Types and Coercion

Bob read two numbers with next(), added them, and got 52 for 5 and 2. Now he wants both answers side by side, the sum and the join, so he never mixes them up again. Read the two tokens with the starter's next() and nextInt().

Input. One line with two tokens a and b, separated by a space. Each token is a decimal number: an optional minus sign, one or more digits, and optionally a decimal point followed by one or more digits. Leading zeros may appear.

Output. Two lines. Line 1 holds the sum of a and b as numbers, printed the way JavaScript prints a number: what String() gives for it. Line 2 holds the two tokens joined as text, a first, exactly as they were typed.

Constraints. Each token has 1 to 25 characters.

Sample. Input 5 2 gives 7 and 52 on two lines.

const input = require("fs").readFileSync(0, "utf8");
const tokens = input.split(/\s+/).filter(Boolean);
let at = 0;
const next = () => tokens[at++];
const nextInt = () => Number(next());
const out = [];

// your code: read with next() and nextInt(), push every line of output to out
// Line 1: a and b added as numbers. Line 2: a and b joined as text.

console.log(out.join("\n"));

Zara gets a list of tokens from a sensor log, and some of them are junk. She wants to know which ones are clean numbers. A token is clean when Number(token) is not NaN. Read the input with the starter's nextInt() and next().

Input. The first line holds n. The second line holds n tokens, separated by spaces. No token contains a space.

Output. n lines, one per token, in the input order. For a clean token, print yes, a space, and the number as JavaScript prints it: String(Number(token)). Otherwise print no.

Constraints. 1 <= n <= 30000. Each token has 1 to 20 characters.

Sample. Input 5 and 12 3.50 abc 007 12px gives yes 12, yes 3.5, no, yes 7 and no on five lines.

const input = require("fs").readFileSync(0, "utf8");
const tokens = input.split(/\s+/).filter(Boolean);
let at = 0;
const next = () => tokens[at++];
const nextInt = () => Number(next());
const out = [];

// your code: read with next() and nextInt(), push every line of output to out
// Read n, then n tokens. Per token: "yes " and the number, or "no".

console.log(out.join("\n"));

Alice is building a pocket calculator for her shop. Each line she types is a number, an operator and another number, and the calculator prints the result. Bob's first version printed 52 for 5 + 2, so Alice wants it done right. Read the input with the starter's nextInt() and next().

Input. The first line holds n, and n lines follow, each a op b: a number, a space, an operator, a space and a number. The operator is one of +, -, * and /. Each number is written in decimal: an optional minus sign, one or more digits, and optionally a decimal point followed by one or more digits. Leading zeros may appear.

Output. n lines. Line i holds the result of a op b for line i, computed on numbers and printed the way JavaScript prints a number. A division by zero prints what JavaScript gives: Infinity, -Infinity or NaN.

Constraints. 1 <= n <= 10000. Each of a and b has 1 to 20 characters.

Sample. Input 5, then 5 + 2, 7 - 10, 6 * 7, 7 / 2 and 1 / 0 on five lines, gives 7, -3, 42, 3.5 and Infinity on five lines.

const input = require("fs").readFileSync(0, "utf8");
const tokens = input.split(/\s+/).filter(Boolean);
let at = 0;
const next = () => tokens[at++];
const nextInt = () => Number(next());
const out = [];

// your code: read with next() and nextInt(), push every line of output to out
// Read n, then n lines of a, op and b. Per line: the result as JavaScript prints it.

console.log(out.join("\n"));

Maria logs three temperature readings a day and wants the largest of each day. Kenji says to call Math.max and be done. This problem trains the ternary operator instead, so the rule is ? : only. Read the input with the starter's nextInt(). Find each largest with ? :, with no Math.max and no if; the judge checks only your output, so that rule is yours to keep.

Input. The first line holds t. Then t lines follow, each with three numbers separated by spaces. Each number is written in decimal: an optional minus sign, one or more digits, and optionally a decimal point followed by one or more digits. Leading zeros may appear.

Output. t lines. Line i holds the largest of the three numbers on input line i, printed the way JavaScript prints a number.

Constraints. 1 <= t <= 10000. Each number has 1 to 20 characters.

Sample. Input 3, then 3 9 4, -5 -2 -9 and 10 9 100, gives 9, -2 and 100 on three lines.

const input = require("fs").readFileSync(0, "utf8");
const tokens = input.split(/\s+/).filter(Boolean);
let at = 0;
const next = () => tokens[at++];
const nextInt = () => Number(next());
const out = [];

// your code: read with next() and nextInt(), push every line of output to out
// Read t, then t lines of three numbers. Per line: the largest, found with ? : only.

console.log(out.join("\n"));

David's sign-up form sends every field as one line of text. A field nobody filled in arrives as null or undefined, and David shows the word default for it. An empty answer is still an answer, and so is 0. This problem uses the lines variant of the starter: const lines = input.split("\n"); replaces the token split, so next() returns the next whole line, empty lines included. Read n with nextInt().

Input. The first line holds n, and n lines follow, one field each. A line that is exactly null stands for the value null. A line that is exactly undefined stands for undefined. Any other line, an empty line included, is the text itself.

Output. n lines, one per field: [, then value ?? "default", then ]. The brackets show every space and every empty text.

Constraints. 1 <= n <= 10000. Each field line has 0 to 60 characters, and the last one is never empty. Every line ends with a newline.

Sample. Input 5, then Alice, null, an empty line, 0 and undefined, gives [Alice], [default], [], [0] and [default] on five lines.

const input = require("fs").readFileSync(0, "utf8");
const lines = input.split("\n");
let at = 0;
const next = () => lines[at++];
const nextInt = () => Number(next());
const out = [];

// your code: read with next() and nextInt(), push every line of output to out
// Lines variant: next() returns the next whole line, empty lines included.
// Read n, then n fields. Per field: "[" + (value ?? "default") + "]".

console.log(out.join("\n"));

Amara copies measurements out of a design file and a shop catalogue, and every one comes with its unit glued on: 12px, 3.5kg. She needs only the number at the start of each token. Read the input with the starter's nextInt() and next().

Input. The first line holds n. The second line holds n tokens, separated by spaces. No token contains a space.

Output. n lines, one per token, in the input order. Print String(parseFloat(token)), or the word invalid when parseFloat(token) is NaN.

Constraints. 1 <= n <= 40000. Each token has 1 to 20 characters.

Sample. Input 5 and 12px 3.5kg -4.5c px12 .5m gives 12, 3.5, -4.5, invalid and 0.5 on five lines.

const input = require("fs").readFileSync(0, "utf8");
const tokens = input.split(/\s+/).filter(Boolean);
let at = 0;
const next = () => tokens[at++];
const nextInt = () => Number(next());
const out = [];

// your code: read with next() and nextInt(), push every line of output to out
// Read n, then n tokens. Per token: the number at its start, or "invalid".

console.log(out.join("\n"));

Maria keeps asking why an empty array counts as true in an if. Zara makes a table of sixteen values with a short name for each. For every name, the program says whether if treats its value as true (truthy) or as false (falsy). Read the input with the starter's nextInt() and next().

Input. The first line holds n. Then n lines follow, each holding one name from this table. Each name stands for the JavaScript value beside it.

Output. n lines, one per name, in the input order: the name, a space, then truthy or falsy.

Constraints. 1 <= n <= 40000. Every name is one of the sixteen in the table, and a name may repeat.

Sample. Input 5, then zero, empty-string, zero-string, empty-array and nan on five lines, gives zero falsy, empty-string falsy, zero-string truthy, empty-array truthy and nan falsy.

const input = require("fs").readFileSync(0, "utf8");
const tokens = input.split(/\s+/).filter(Boolean);
let at = 0;
const next = () => tokens[at++];
const nextInt = () => Number(next());
const out = [];

// your code: read with next() and nextInt(), push every line of output to out
// Read n, then n names. Per name: the name, a space, then truthy or falsy.

console.log(out.join("\n"));

Kenji's code review says "never use ==". Maria wants to see what == actually does, next to === and Object.is, for any two values. Zara writes each value as a typed token, so a program can build the value back from the text. Read the input with the starter's nextInt() and next(). token.slice(4) gives the part of a token after its first four characters, such as the text after num:; Module 3 teaches slice.

Input. The first line holds n. Then n lines follow, each with two tokens x and y, separated by a space. A token is one of these:

• num: and a text: the number Number(text), such as num:-0, num:NaN or num:Infinity;
• str: and a text: the string text itself, and str: alone is the empty string "";
• bool:true or bool:false: the boolean;
• null or undefined: that value.

Output. n lines. Line i holds three words for the pair on input line i: x == y, x === y and Object.is(x, y), each true or false, separated by single spaces.

Constraints. 1 <= n <= 20000. Each token has at most 25 characters and no spaces. The text after num: is never empty.

Sample. The sample is the twelve pairs of lesson 04's chart. Input 12, then num:1 str:1, num:0 str:, num:0 str:0, str: str:0, null undefined, null num:0, undefined num:0, num:NaN num:NaN, num:0 num:-0, bool:true num:1, bool:true str:true and bool:false str:0 on twelve lines. It gives true false false three times, false false false, true false false, false false false twice, false false true, true true false, true false false, false false false and true false false.

const input = require("fs").readFileSync(0, "utf8");
const tokens = input.split(/\s+/).filter(Boolean);
let at = 0;
const next = () => tokens[at++];
const nextInt = () => Number(next());
const out = [];

// your code: read with next() and nextInt(), push every line of output to out
// Read n, then n lines of two typed tokens such as num:1 and str:1.
// Per line: x == y, x === y and Object.is(x, y), separated by spaces.

console.log(out.join("\n"));

Bob's form reader writes value || "missing", and his report says missing for a quantity of 0 and for a field left empty. Amara wants three different words for three different things: nothing arrived, an empty answer arrived, and a zero arrived. This problem uses the lines variant of the starter: const lines = input.split("\n"); replaces the token split, so next() returns the next whole line, empty lines included. Read n with nextInt().

Input. The first line holds n, and n lines follow. Decode each line into a value, in this order. A line that is exactly null is null, and exactly undefined is undefined. An empty line is the empty string "". Any other line is Number(line) when that is not NaN, and otherwise the line's text.

Output. n lines, one per value. Print missing when value == null, empty when value === "", and zero when value === 0. Otherwise print value, a space and String(value).

Constraints. 1 <= n <= 20000. Each of the n lines has 0 to 20 characters, never starts or ends with a space, and the last one is never empty.

Sample. Input 7, then null, 0, an empty line, 12, abc, undefined and -0, gives missing, zero, empty, value 12, value abc, missing and zero on seven lines.

const input = require("fs").readFileSync(0, "utf8");
const lines = input.split("\n");
let at = 0;
const next = () => lines[at++];
const nextInt = () => Number(next());
const out = [];

// your code: read with next() and nextInt(), push every line of output to out
// Lines variant: next() returns the next whole line, empty lines included.
// Decode each line, then print missing, empty, zero or value and the value.

console.log(out.join("\n"));

Zara's game server keeps every player's points as a whole number, up to 10¹⁸ each. The season total is the sum of them all. Added as ordinary numbers, the total loses its last digits once it passes 2⁵³, so Zara wants it exact. Read n with the starter's nextInt() and each integer with next().

Input. The first line holds n. The second line holds n integers, separated by spaces. Each integer is written in decimal, with an optional + or - sign, and leading zeros may appear.

Output. One line with the exact sum of the n integers, in decimal, with a minus sign when it is negative.

Constraints. 1 <= n <= 40000. Each integer is between -1000000000000000000 and 1000000000000000000, which is 10¹⁸.

Sample. Input 3 and 9007199254740991 9007199254740991 1 gives 18014398509481983.

const input = require("fs").readFileSync(0, "utf8");
const tokens = input.split(/\s+/).filter(Boolean);
let at = 0;
const next = () => tokens[at++];
const nextInt = () => Number(next());
const out = [];

// your code: read with next() and nextInt(), push every line of output to out
// Read n, then n integers. Print their exact sum: BigInt, not Number.

console.log(out.join("\n"));