[doitduri] Week 07 solutions

longest-substring-without-repeating-characters/doitduri.swift

@@ -0,0 +1,20 @@
+class Solution {
+    func lengthOfLongestSubstring(_ s: String) -> Int {
+        var charIndexMap = [Character: Int]()
+        var maxLength = 0
+        var startIndex = 0
+
+        for (i, char) in Array(s).enumerated() {
+            if let lastIndex = charIndexMap[char], lastIndex >= startIndex {
+                startIndex = lastIndex + 1
+            }
+
+            let currentLength = i - startIndex + 1
+            maxLength = max(maxLength, currentLength)
+
+            charIndexMap[char] = i
+        }
+
+        return maxLength
+    }
+}

number-of-islands/doitduri.swift

@@ -0,0 +1,34 @@
+class Solution {
+    func numIslands(_ grid: [[Character]]) -> Int {
+        guard !grid.isEmpty else { return 0 }
+
+        let rows = grid.count
+        let colums = grid[0].count
+        var visited = grid
+        var islandCount = 0
+
+        func dfs(_ row: Int, _ col: Int) {
+            guard row >= 0 && row < rows && col >= 0 && col < colums && visited[row][col] == "1" else {
+                return
+            }
+
+            visited[row][col] = "0"
+
+            dfs(row - 1, col)
+            dfs(row + 1, col)
+            dfs(row, col - 1)
+            dfs(row, col + 1)
+        }
+
+        for row in 0..<rows {
+            for col in 0..<colums {
+                if visited[row][col] == "1" {
+                    islandCount += 1
+                    dfs(row, col)
+                }
+            }
+        }
+
+        return islandCount
+    }
+}

reverse-linked-list/doitduri.swift

@@ -0,0 +1,14 @@
+class Solution {
+    func reverseList(_ head: ListNode?) -> ListNode? {
+        var current = head, previous: ListNode? = nil
+
+        while current != nil {
+            let next = current?.next
+            current?.next = previous
+            previous = current
+            current = next
+        }
+
+        return previous
+    }
+}

set-matrix-zeroes/doitduri.swift

@@ -0,0 +1,60 @@
+class Solution {
+    func setZeroes(_ matrix: inout [[Int]]) {
+    let m = matrix.count
+    let n = matrix[0].count
+
+    var firstRowHasZero = false
+    var firstColHasZero = false
+
+    for i in 0..<m {
+        if matrix[i][0] == 0 {
+            firstColHasZero = true
+            break
+        }
+    }
+
+    for j in 0..<n {
+        if matrix[0][j] == 0 {
+            firstRowHasZero = true
+            break
+        }
+    }
+
+    for i in 1..<m {
+        for j in 1..<n {
+            if matrix[i][j] == 0 {
+                matrix[i][0] = 0
+                matrix[0][j] = 0
+            }
+        }
+    }
+
+    for i in 1..<m {
+        if matrix[i][0] == 0 {
+            for j in 1..<n {
+                matrix[i][j] = 0
+            }
+        }
+    }
+
+    for j in 1..<n {
+        if matrix[0][j] == 0 {
+            for i in 1..<m {
+                matrix[i][j] = 0
+            }
+        }
+    }
+
+    if firstRowHasZero {
+        for j in 0..<n {
+            matrix[0][j] = 0
+        }
+    }
+
+    if firstColHasZero {
+        for i in 0..<m {
+            matrix[i][0] = 0
+        }
+    }
+    }
+}

unique-paths/doitduri.swift

@@ -0,0 +1,21 @@
+class Solution {
+    func uniquePaths(_ m: Int, _ n: Int) -> Int {
+        var dp = Array(repeating: Array(repeating: 0, count: n), count: m)
+
+        for j in 0..<n {
+            dp[0][j] = 1
+        }
+
+        for i in 0..<m {
+            dp[i][0] = 1
+        }
+
+        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]
+    }
+}