Merge pull request #193 from WhiteHyun/whitehyun/week12

[Hyun] Week 12 Solution Explanation

Author: WhiteHyun

jump-game/WhiteHyun.swift

@@ -0,0 +1,19 @@
+//  
+//  55. Jump Game
+//  https://leetcode.com/problems/jump-game/description/
+//  Dale-Study
+//  
+//  Created by WhiteHyun on 2024/07/20.
+//  
+
+class Solution {
+  func canJump(_ numbers: [Int]) -> Bool {
+    var goal = numbers.endIndex - 1
+
+    for index in numbers.indices.dropLast().reversed() where index + numbers[index] >= goal {
+      goal = index
+    }
+
+    return goal == 0
+  }
+}

longest-common-subsequence/WhiteHyun.swift

@@ -0,0 +1,31 @@
+//  
+//  1143. Longest Common Subsequence
+//  https://leetcode.com/problems/longest-common-subsequence/description/
+//  Dale-Study
+//  
+//  Created by WhiteHyun on 2024/07/20.
+//  
+
+class Solution {
+  func longestCommonSubsequence(_ text1: String, _ text2: String) -> Int {
+    let m = text1.count
+    let n = text2.count
+
+    var dp: [[Int]] = .init(repeating: .init(repeating: 0, count: n + 1), count: m + 1)
+
+    let text1Array = Array(text1)
+    let text2Array = Array(text2)
+
+    for i in 1 ... m {
+      for j in 1 ... n {
+        if text1Array[i - 1] == text2Array[j - 1] {
+          dp[i][j] = dp[i - 1][j - 1] + 1
+        } else {
+          dp[i][j] = max(dp[i - 1][j], dp[i][j - 1])
+        }
+      }
+    }
+
+    return dp[m][n]
+  }
+}

longest-increasing-subsequence/WhiteHyun.swift

@@ -0,0 +1,38 @@
+//  
+//  300. Longest Increasing Subsequence
+//  https://leetcode.com/problems/longest-increasing-subsequence/description/
+//  Dale-Study
+//  
+//  Created by WhiteHyun on 2024/07/20.
+//  
+
+class Solution {
+  func lengthOfLIS(_ nums: [Int]) -> Int {
+    var tails: [Int] = [nums[0]]
+
+    for index in 1 ..< nums.count {
+      if nums[index] > tails.last! {
+        tails.append(nums[index])
+      } else {
+        tails[binarySearch(tails, target: nums[index])] = nums[index]
+      }
+    }
+
+    return tails.count
+  }
+
+  private func binarySearch(_ arr: [Int], target: Int) -> Int {
+    var left = 0
+    var right = arr.count - 1
+
+    while left <= right {
+      let mid = (left + right) >> 1
+      if arr[mid] < target {
+        left = mid + 1
+      } else {
+        right = mid - 1
+      }
+    }
+    return left
+  }
+}

maximum-subarray/WhiteHyun.swift

@@ -0,0 +1,22 @@
+//  
+//  53. Maximum Subarray
+//  https://leetcode.com/problems/maximum-subarray/description/
+//  Dale-Study
+//  
+//  Created by WhiteHyun on 2024/07/20.
+//  
+
+class Solution {
+  func maxSubArray(_ numbers: [Int]) -> Int {
+    var tracking = numbers[0]
+    var answer = numbers[0]
+    for value in numbers.dropFirst() {
+      tracking = max(tracking + value, value)
+      if tracking > answer {
+        answer = tracking
+      }
+    }
+
+    return answer
+  }
+}

unique-paths/WhiteHyun.swift

@@ -0,0 +1,22 @@
+//  
+//  62. Unique Paths
+//  https://leetcode.com/problems/unique-paths/description/
+//  Dale-Study
+//  
+//  Created by WhiteHyun on 2024/07/20.
+//  
+
+class Solution {
+  func uniquePaths(_ m: Int, _ n: Int) -> Int {
+    if m == 1 || n == 1 { return 1 }
+    var dp: [[Int]] = .init(repeating: .init(repeating: 1, count: n), count: m)
+
+    for i in 1 ..< m {
+      for j in 1 ..< n {
+        dp[i][j] = dp[i - 1][j] + dp[i][j - 1]
+      }
+    }
+
+    return dp[m - 1][n - 1]
+  }
+}