Merge pull request #18 from programmingbookclub/meetup-25

LeetCode 讀書會第 25 次聚會

Author: ytyubox

紀錄/25 20210420.md

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+# LeetCode 讀書會第 25 次聚會 2021/04/20
+
+  leetcode 讀書會通知
+ 1. 項目: 第 25 次聚會
+ 2. 目的: 線上一起寫題目, 由有想法的人帶領, 先解題, 再看該題有趣的解法
+ 3. 時間: 4/20 (二) 20:00 ~ 21:00
+ 4. 地點: google meet 線上 (前 10 分鐘預備鏈接)
+ 5. 解題項目:  [Binary search](https://leetcode.com/explore/learn/card/binary-search)
+ 6. 共筆: GitHub https://github.com/programmingbookclub/Leetcode-club
+ 7. 備註: 上次有稍微聊一下 658 題目，這次會重頭開始聊658，會強調如何理解題目、題目預期的答案，與如何實作。 
+
+last weak 
+```swift=
+class Solution {
+    func searchRange(_ nums: [Int], _ target: Int) -> [Int] {
+        let m = { l, u -> Int in
+            var (l, u) = (l, u)
+            while true {
+                if l >= u { return -1 }
+                let m = mid(l, u), mnb = nums[m]
+                if mnb == target { return m }
+                if mnb < target { l = m + 1 }
+                if mnb > target { u = m }
+            }
+
+        }(0, nums.count)
+        
+        if m == -1 { return [-1, -1] }
+        
+        let l = { l, u -> Int in
+            var (l, u) = (l, u)
+            while true {
+                if nums[l] == target { return l }
+                let m = mid(l, u), mnb = nums[m]
+                if mnb == target, nums[m - 1] != target { return m }
+                if mnb == target { u = m - 1 }
+                else { l = m + 1 }
+            }
+
+        }(0, m - 1)
+
+        let u = { l, u -> Int in
+            var (l, u) = (l, u)
+            while true {
+                if nums[u] == target { return u }
+                let m = mid(l, u), mnb = nums[m]
+                if mnb == target, nums[m + 1] != target { return m }
+                if mnb == target { l = m + 1 }
+                else { u = m - 1 }
+            }
+
+        }(m + 1, nums.count - 1)
+
+        return [l, u]
+    }
+}
+
+func mid(_ s: Int, _ b: Int) -> Int {
+    (b - s) / 2 + s
+}
+
+```
+
+* MEDIUM	 658	 Find K Closest Elements	 https://leetcode.com/problems/find-k-closest-elements
+
+```typescript
+// `Search for a Range` in TypeScript by iteration and resursion mixed
+// Time Complexity: O(log n), Space Complexity: O(1)
+//  by louis222220 
+function searchRange(nums: number[], target: number): number[] {
+  let left = 0;
+  let right = nums.length - 1;
+  let middle: number;
+  while (left <= right) {
+    middle = getMiddleIndex(left, right);
+    if (nums[middle] === target) {
+      const leftTargerBoundary = searchLeftTargetBoundary(left, middle);
+      const rightTargetBoundary = searchRightTargetBoundary(middle, right);
+      
+      const result = [leftTargerBoundary, rightTargetBoundary];
+      return result;
+    }
+    else if (nums[middle] > target) right = middle - 1;
+    else left = middle + 1;
+  }
+  return [-1, -1];
+  
+  // helper functions
+  function getMiddleIndex(left: number, right: number) {
+    if (left > right) return -1;
+    if (left === right) return left;
+    return left + Math.floor((right - left) / 2);
+  }
+  /** Search left boundary of target by Recursion */
+  function searchLeftTargetBoundary(left: number, right: number) {
+    if (nums[left] === target) return left;
+    const middle = getMiddleIndex(left, right);
+    
+    if (nums[middle] === target && nums[middle - 1] !== target) return middle;
+    else if (nums[middle] !== target) return searchLeftTargetBoundary(middle + 1, right);
+    else return searchLeftTargetBoundary(left, middle - 1);
+  }
+  /** Search right boundary of target by Recursion */
+  function searchRightTargetBoundary(left: number, right: number) {
+    if (nums[right] === target) return right;
+    const middle = getMiddleIndex(left, right);
+    
+    if (nums[middle] === target && nums[middle + 1] !== target) return middle;
+    else if (nums[middle] !== target) return searchRightTargetBoundary(left, middle - 1);
+    else return searchRightTargetBoundary(middle + 1, right);
+  }
+};
+```
+
+* MEDIUM	 162	 Find Peak Element	 https://leetcode.com/problems/find-peak-element
+
+* Template Analysis
+
+* Article Binary Search Template Analysis
+
+* 🔓	 EASY	 270	 Closest Binary Search Tree Value	 https://leetcode.com/problems/closest-binary-search-tree-value
+
+```typescript=
+/** 
+  嘗試找到 arr[m]，符合 (x - arr[m]) > (arr[m + k] - x)，m 即為解的第一個元素，
+  而尋找的過程就可以使用二元搜尋法
+  Inspired by [Clean O(logN) solution in Python](https://leetcode.com/explore/learn/card/binary-search/135/template-iii/945/discuss/133604/Clean-O(logN)-solution-in-Python)
+  Time Complexity: O( log(n) + k ), Space Complexity: O(k)
+  k ==> result's first element in original array's index
+  [i ..< i+k] --> 是 result Array
+*/
+function findClosestElements(arr: number[], k: number, x: number): number[] {
+  if (k === arr.length) return arr;
+  let left = 0;
+  let right = arr.length - k;
+  let middle = left + Math.floor((right - left) / 2);
+  while(left < right) {
+    /** middle 與 x 的差 */
+    const middleToX = x - arr[middle];
+    /** x 與 middleK 的差，middleK 為 middle + k 的位置 */
+    const xToMiddleK = arr[middle + k] - x;
+
+    // arr[middle] 離 x 比較遠，繼續檢查 middle 的右側
+    if (middleToX > xToMiddleK) left = middle + 1;
+    // arr[middle] 離 x 比較近，繼續檢查 middle 的左側
+    else right = middle;
+    middle = left + Math.floor((right - left) / 2);
+  }
+  return arr.slice(middle, middle + k);
+};
+```
+
+* 🔓	 MEDIUM	 702	 Search in a Sorted Array of Unknown Size	 https://leetcode.com/problems/search-in-a-sorted-array-of-unknown-size
+
+* Conclusion
+
+* MEDIUM	 50	 Pow(x, n)	 https://leetcode.com/problems/powx-n
+
+```typescript
+/** Recursion in TS by Louis. It's inspired by [the discussion](https://leetcode.com/explore/learn/card/binary-search/137/conclusion/982/discuss/19546/Short-and-easy-to-understand-solution) */
+function myPow(x: number, n: number): number {
+  if (n == 0) return 1;
+  if (n < 0) return myPow(1 / x, -n);
+  if (n % 2 == 0) return myPow(x * x, n / 2);
+  else return x * myPow(x * x, Math.floor(n / 2));
+};
+
+```typescript
+/** Iteration in TS by Louis */
+function myPow(x: number, n: number): number {
+  let base = x;
+  let exponent = n;
+  let constant = 1;
+  
+  if (n === 0) return 1;
+  
+  if (n < 0) {
+    base = 1 / x;
+    exponent = -n;
+  }
+  
+  while (exponent > 1) {
+    if (exponent % 2 == 0) {
+      base = base * base;
+      exponent = exponent / 2;
+    }
+    else {
+      constant = constant * base;
+      base = base * base;
+      exponent = Math.floor(exponent / 2);
+    }
+  }
+  
+  return constant * base;
+}
+
+
+* EASY	 367	 Valid Perfect Square	 https://leetcode.com/problems/valid-perfect-square
+
+```typescript
+/** Iteration for `Valid Perfect Square` in TS by Louis*/
+function isPerfectSquare(num: number): boolean {
+  if (num === 1) return true;
+  
+  let lower = 2;
+  let upper = Math.floor(num / 2);
+  
+  while (lower <= upper) {
+    const middle = lower + Math.floor((upper - lower) / 2);
+    if (num === middle * middle) return true;
+    else if (num > middle * middle) lower = middle + 1;
+    else upper = middle - 1;
+  }
+  return false;
+};
+
+* EASY	 744	 Find Smallest Letter Greater Than Target	 https://leetcode.com/problems/find-smallest-letter-greater-than-target
+
+* More Practices
+
+* MEDIUM	 153	 Find Minimum in Rotated Sorted Array	 https://leetcode.com/problems/find-minimum-in-rotated-sorted-array
+
+* HARD	 154	 Find Minimum in Rotated Sorted Array II	 https://leetcode.com/problems/find-minimum-in-rotated-sorted-array-ii
+
+* EASY	 349	 Intersection of Two Arrays	 https://leetcode.com/problems/intersection-of-two-arrays
+
+* EASY	 350	 Intersection of Two Arrays II	 https://leetcode.com/problems/intersection-of-two-arrays-ii
+
+* EASY	 167	 Two Sum II - Input array is sorted	 https://leetcode.com/problems/two-sum-ii-input-array-is-sorted
+
+* More Practices II
+
+* MEDIUM	 287	 Find the Duplicate Number	 https://leetcode.com/problems/find-the-duplicate-number
+
+* HARD	 4	 Median of Two Sorted Arrays	 https://leetcode.com/problems/median-of-two-sorted-arrays
+
+* HARD	 719	 Find K-th Smallest Pair Distance	 https://leetcode.com/problems/find-k-th-smallest-pair-distance 
+
+* HARD	 410	 Split Array Largest Sum	 https://leetcode.com/problems/split-array-largest-sum