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array.reverse.js
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116 lines (102 loc) · 2.54 KB
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/*
* @title: Reverse Array
* @description: Simple function to reverse array
* @author: Thorsten Kober
* @email: [email protected]
*/
// while loop - left / right pointers
// time complexity O(n)
// space complexity O(1)
function reverse1(arr) {
let left = 0;
let right = arr.length - 1;
while (left < right) {
const temp = arr[left];
arr[left] = arr[right];
arr[right] = temp;
left++;
right--;
}
return arr;
}
// for loop
// time complexity O(n)
// space complexity O(1)
function reverse2(arr) {
const len = arr.length;
const middle = Math.floor(len / 2);
for (let i = 0; i < middle; i++) {
const temp = arr[i];
arr[i] = arr[len - 1 - i];
arr[len - 1 - i] = temp;
}
return arr;
}
// array destructuring
// time complexity O(n)
// space complexity O(1)
function reverse3(arr) {
const len = arr.length;
const middle = Math.floor(len / 2);
for (let i = 0; i < middle; i++) {
[arr[i], arr[len - 1 - i]] = [arr[len - 1 - i], arr[i]];
}
return arr;
}
// for loop backwards - extra array
// time complexity O(n)
// space complexity O(n)
function reverse4(arr) {
const result = [];
for (let i = arr.length - 1; i >= 0; i--) {
result.push(arr[i]);
}
return result;
}
// for loop forward - extra array
// time complexity O(n)
// space complexity O(n)
function reverse5(arr) {
const result = [];
for (let i = 0; i < arr.length; i++) {
result.push(arr[arr.length - 1 - i]);
}
return result;
}
// recursion
// time complexity O(n)
// space complexity O(n)
function reverse6(arr) {
if (arr.length === 0) {
return [];
}
// return [arr.pop()].concat(reverse6(arr));
return [arr.pop(), ...reverse6(arr)];
}
// npx jest algorithms/array/array.reverse.js
describe('reverse array', () => {
test('reverse1()', () => {
const nums = [1, 2, 3, 4, 5, 6, 7];
expect(reverse1(nums)).toEqual([7, 6, 5, 4, 3, 2, 1]);
});
test('reverse2()', () => {
const nums = [1, 2, 3, 4, 5, 6, 7];
expect(reverse2(nums)).toEqual([7, 6, 5, 4, 3, 2, 1]);
});
test('reverse3()', () => {
const nums = [1, 2, 3, 4, 5, 6, 7];
expect(reverse3(nums)).toEqual([7, 6, 5, 4, 3, 2, 1]);
});
test('reverse4()', () => {
const nums = [1, 2, 3, 4, 5, 6, 7];
expect(reverse4(nums)).toEqual([7, 6, 5, 4, 3, 2, 1]);
});
test('reverse5()', () => {
const nums = [1, 2, 3, 4, 5, 6, 7];
expect(reverse5(nums)).toEqual([7, 6, 5, 4, 3, 2, 1]);
});
test('reverse6()', () => {
const nums = [1, 2, 3, 4, 5, 6, 7];
expect(reverse6(nums)).toEqual([7, 6, 5, 4, 3, 2, 1]);
});
});