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LeetCode May 2020
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// LeetCode May 2020 |
Author
wovalle
commented
May 21, 2020
// 16.js
/**
* Definition for singly-linked list.
* function ListNode(val, next) {
* this.val = (val===undefined ? 0 : val)
* this.next = (next===undefined ? null : next)
* }
*/
/**
* @param {ListNode} head
* @return {ListNode}
*/
var oddEvenList = function(head) {
if(!head) return null
let [node, nextEven, evens] = [head, head.next, head.next]
while(nextEven !== null && nextEven.next !== null) {
node.next = node.next.next
node = node.next
nextEven.next = node.next
nextEven = nextEven.next
}
node.next = evens
return head
};
// Time: O(n)
// Space: O(1) (I'm just saving the references for the even nodes)
// 17.js
const getCode = (s, i) => s.charCodeAt(i) - 'a'.charCodeAt(0);
const areEqualArrays = (a1, a2) => {
for (let i = 0; i <= a1.length; i++) {
if (a1[i] !== a2[i]) {
return false;
}
}
return true;
};
const findAnagrams = (p, s) => {
const freqS = new Array(26).fill(0);
const freqP = new Array(26).fill(0);
const answer = [];
for (let i = 0; i < s.length; i++) {
freqS[getCode(s, i)]++;
}
for (let i = 0; i < s.length; i++) {
freqP[getCode(p, i)]++;
}
for (let i = s.length; i < p.length; i++) {
if (areEqualArrays(freqS, freqP)) {
answer.push(i - s.length);
}
freqP[getCode(p, i)]++;
freqP[getCode(p, i - s.length)]--;
}
if (areEqualArrays(freqS, freqP)) {
answer.push(p.length - s.length);
}
return answer;
};
// Time: O(S + P) = O(n)
// Space: O(1)
// 18.js
var checkInclusion = function (s1, s2) {
if (s1.length > s2.length) {
return false;
}
const freq = new Array(26).fill(0);
const base = 'a'.charCodeAt(0);
const getCode = (s, i) => s.charCodeAt(i) - base;
const areEqualArrays = (a1, a2) => {
for (let i = 0; i <= a1.length; i++) {
if (a1[i] !== a2[i]) {
return false;
}
}
return true;
};
for (let i = 0; i < s1.length; i++) {
freq[getCode(s1, i)]++;
}
for (let i = 0; i < s2.length; i++) {
if (freq[getCode(s2, i)] > 0) {
const currentFreq = new Array(26).fill(0);
for (let j = i; j < s2.length; j++) {
const currentCode = getCode(s2, j);
currentFreq[currentCode]++;
// if we find another character before length, just discard the positions
if (freq[currentCode] === 0) {
i = j;
break;
}
if (j - i < s1.length - 1) {
continue;
}
if (areEqualArrays(freq, currentFreq)) {
return true;
} else {
currentFreq[getCode(s2, j - s1.length + 1)]--;
}
}
}
}
return false;
};
// Time: O(n)
// Space: O(n)
// 19.js
class StockSpanner {
max = -Infinity;
maxCount = 0;
localMax = [];
next(stock) {
const peek = (arr) => arr[arr.length - 1];
if (stock >= this.max) {
this.max = stock;
const localMax = this.localMax.length
? this.localMax.reduce((acc, cur) => (acc += cur[1]), 0)
: 0;
this.maxCount = this.maxCount + localMax + 1;
this.localMax = [];
return this.maxCount;
}
let localCount = 1;
while (this.localMax.length && stock >= peek(this.localMax)[0]) {
const [_, count] = this.localMax.pop();
localCount += count;
}
this.localMax.push([stock, localCount]);
return localCount;
}
}
// Time: O(n)
// Space: O(n)
// 20.js
var kthSmallest = function (root, k) {
let stack = [root];
let node = root;
while (stack.length) {
while (node) {
stack.push(node);
node = node.left;
}
node = stack.pop();
if (k === 1) {
return node.val;
} else {
k--;
}
node = node.right;
}
return null;
};
// Time: O(n)
// Space: O(n)
// 21.js
/**
* @param {number[][]} matrix
* @return {number}
*/
const isValidSubMatrix = (matrix, x, y, side) => {
if (y + side > matrix.length || x + side > matrix[y].length) {
return false;
}
if (side === 1) {
return matrix[y][x] === 1;
}
for (let sy = y; sy < y + side; sy++) {
for (let sx = x; sx < x + side; sx++) {
if (!matrix[sy][sx]) {
return false;
}
}
}
return true;
};
var countSquares = function (matrix) {
const times = Math.min(matrix.length, matrix[0].length);
let number = 0;
for (let side = 1; side <= times; side++) {
for (let y = 0; y < matrix.length; y++) {
for (let x = 0; x < matrix[y].length; x++) {
if (isValidSubMatrix(matrix, x, y, side)) {
number++;
}
}
}
}
return number;
};
// Time: O(n ^ 3) or O(n ^ 4), lol
// Space: O(1)
// 22.js
/**
* @param {string} s
* @return {string}
*/
var frequencySort = function(s) {
// It would be nice if we had some type of ordered Map
// to prevent the sort in line 15
const freq = {}
for (let letter of s) {
freq[letter] = (freq[letter] || 0) + 1
}
return Object.entries(freq)
.sort((a, b) => b[1] - a[1])
.map(e => e[0].repeat(e[1]))
.join('')
};
// Time: O(n)
// Space: O(n)
// 23.js
/**
* @param {number[][]} A
* @param {number[][]} B
* @return {number[][]}
*/
var intervalIntersection = function(A, B) {
const getIntersection = (a, b) => {
if (a[1] < b[0] || a[0] > b[1])
return null
return [Math.max(a[0], b[0]), Math.min(a[1], b[1])]
}
let pivotA = 0
let pivotB = 0
const answer = []
while (pivotA < A.length && pivotB < B.length) {
const intersection = getIntersection(A[pivotA], B[pivotB])
if(intersection) {
answer.push(intersection)
}
if(A[pivotA][1] < B[pivotB][1]) {
pivotA++
} else {
pivotB++
}
}
return answer
};
// Time: O(A + B) = O(n)
// Space: O(N)
// 24.js
const getLast = (arr, level = 1) => (arr.length ? arr[arr.length - level] : null);
const bstFromPreorder = function (preorder) {
if (!preorder.length) {
return null;
}
const leaves = [[new TreeNode(preorder.shift()), -Infinity, Infinity]];
while (preorder.length) {
const currentVal = preorder.shift();
while (currentVal > getLast(leaves)[2] || currentVal < getLast(leaves)[1]) {
leaves.pop();
}
const [leave, min, max] = getLast(leaves);
if (currentVal > leave.val) {
leave.right = new TreeNode(currentVal);
leaves.push([leave.right, leave.val, max]);
} else if (currentVal < leave.val) {
leave.left = new TreeNode(currentVal);
leaves.push([leave.left, min, leave.val]);
}
}
return leaves[0][0];
};
// Time: O(n)
// Space: O(n)
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