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[hoyeongkwak] week 10 solutions #1560

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Jun 9, 2025
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25 changes: 25 additions & 0 deletions course-schedule/hoyeongkwak.ts
Original file line number Diff line number Diff line change
@@ -0,0 +1,25 @@
function canFinish(numCourses: number, prerequisites: number[][]): boolean {
const graph: number[][] = Array.from({ length: numCourses }, () => [])
for (const [course, prereq] of prerequisites) {
graph[course].push(prereq)
}
const traversing = new Set<number>()
const finished = new Set<number>()

const finish = (crs: number): boolean => {
if (traversing.has(crs)) return false
if (finished.has(crs)) return true

traversing.add(crs)
for (const pre of graph[crs]) {
if (!finish(pre)) return false
}
traversing.delete(crs)
finished.add(crs)
return true
}
for (let crs = 0; crs < numCourses; crs++) {
if (!finish(crs)) return false
}
return true
};
24 changes: 24 additions & 0 deletions invert-binary-tree/hoyeongkwak.ts
Original file line number Diff line number Diff line change
@@ -0,0 +1,24 @@
/**
* Definition for a binary tree node.
* class TreeNode {
* val: number
* left: TreeNode | null
* right: TreeNode | null
* constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
* this.val = (val===undefined ? 0 : val)
* this.left = (left===undefined ? null : left)
* this.right = (right===undefined ? null : right)
* }
* }
*/

function invertTree(root: TreeNode | null): TreeNode | null {
if (root == null) return null
const temp = root.left
root.left = root.right
root.right = temp

invertTree(root.left)
invertTree(root.right)
return root
};
19 changes: 19 additions & 0 deletions jump-game/hoyeongkwak.ts
Original file line number Diff line number Diff line change
@@ -0,0 +1,19 @@
function canJump(nums: number[]): boolean {
const memo: boolean[] = new Array(nums.length).fill(null)
const dfs = (start: number): boolean => {
if (start >= nums.length - 1) {
return true
}
if (memo[start] != null) return memo[start]
const maxJump = nums[start]
for (let i = 1; i <= maxJump; i++) {
if (dfs(start + i)) {
memo[start] = true
return true
}
}
memo[start] = false
return false
}
return dfs(0)
};
27 changes: 27 additions & 0 deletions merge-k-sorted-lists/hoyeongkwak.ts
Original file line number Diff line number Diff line change
@@ -0,0 +1,27 @@
/**
* Definition for singly-linked list.
* class ListNode {
* val: number
* next: ListNode | null
* constructor(val?: number, next?: ListNode | null) {
* this.val = (val===undefined ? 0 : val)
* this.next = (next===undefined ? null : next)
* }
* }
*/

function mergeKLists(lists: Array<ListNode | null>): ListNode | null {
const tempArray: Array<ListNode> = []
lists.forEach((node) => {
while (node) {
tempArray.push(node)
node = node.next
}
})
tempArray.sort((node1, node2) => node1.val - node2.val)
let result = tempArray[0] ?? null
tempArray.forEach((node, index, arr) => {
node.next = arr[index + 1] ?? null
})
return result
};
27 changes: 27 additions & 0 deletions search-in-rotated-sorted-array/hoyeongkwak.ts
Original file line number Diff line number Diff line change
@@ -0,0 +1,27 @@
function search(nums: number[], target: number): number {
// return nums.indexOf(target)
let left = 0
let right = nums.length - 1

while (left <= right) {
const mid = Math.floor((left + right) / 2)
if (nums[mid] === target) {
return mid
}

if (nums[left] <= nums[mid]) {
if (target >= nums[left] && target < nums[mid]) {
right = mid - 1
} else {
left = mid + 1
}
} else {
if (target > nums[mid] && target <= nums[right]) {
left = mid + 1
} else {
right = mid - 1
}
}
}
return -1
};