[tedkimdev] WEEK 07 Solutions

longest-substring-without-repeating-characters/tedkimdev.go

@@ -0,0 +1,19 @@
+// TC: O(n)
+// SC: O(m)
+func lengthOfLongestSubstring(s string) int {
+	charIndex := map[byte]int{}
+
+	maxLen := 0
+	left := 0
+	for right := 0; right < len(s); right++ {
+		if idx, ok := charIndex[s[right]]; ok && idx >= left {
+			left = idx + 1
+		}
+		charIndex[s[right]] = right
+		if right-left+1 > maxLen {
+			maxLen = right - left + 1
+		}
+	}
+
+	return maxLen
+}

number-of-islands/tedkimdev.go

@@ -0,0 +1,31 @@
+// TC: O(m * n)
+// SC: O(m * n)
+func numIslands(grid [][]byte) int {
+	rows, cols := len(grid), len(grid[0])
+	islands := 0
+
+	var dfs func(r, c int)
+	dfs = func(r, c int) {
+		if r < 0 || c < 0 ||
+			r >= rows || c >= cols ||
+			grid[r][c] == '0' {
+			return
+		}
+		grid[r][c] = '0'
+		dfs(r+1, c)
+		dfs(r-1, c)
+		dfs(r, c+1)
+		dfs(r, c-1)
+	}
+
+	for r := 0; r < rows; r++ {
+		for c := 0; c < cols; c++ {
+			if grid[r][c] == '1' {
+				dfs(r, c)
+				islands++
+			}
+		}
+	}
+
+	return islands
+}

reverse-linked-list/tedkimdev.go

@@ -0,0 +1,22 @@
+/**
+ * Definition for singly-linked list.
+ * type ListNode struct {
+ *     Val int
+ *     Next *ListNode
+ * }
+ */
+
+// TC: O(n)
+// SC: O(1)
+func reverseList(head *ListNode) *ListNode {
+	var prev *ListNode
+	cur := head
+
+	for cur != nil {
+		temp := cur.Next
+		cur.Next = prev
+		prev = cur
+		cur = temp
+	}
+	return prev
+}

set-matrix-zeroes/tedkimdev.go

@@ -0,0 +1,40 @@
+// TC: O(m * n)
+// SC: O(1)
+func setZeroes(matrix [][]int) {
+	rowNum, colNum := len(matrix), len(matrix[0])
+
+	firstRowIsZero := false
+
+	for r := 0; r < rowNum; r++ {
+		for c := 0; c < colNum; c++ {
+			if matrix[r][c] == 0 {
+				matrix[0][c] = 0
+				if r > 0 {
+					matrix[r][0] = 0
+				} else {
+					firstRowIsZero = true
+				}
+			}
+		}
+	}
+
+	for r := 1; r < rowNum; r++ {
+		for c := 1; c < colNum; c++ {
+			if matrix[r][0] == 0 || matrix[0][c] == 0 {
+				matrix[r][c] = 0
+			}
+		}
+	}
+
+	if matrix[0][0] == 0 { // first column is zero
+		for r := 0; r < rowNum; r++ {
+			matrix[r][0] = 0
+		}
+	}
+
+	if firstRowIsZero {
+		for c := 0; c < colNum; c++ {
+			matrix[0][c] = 0
+		}
+	}
+}

unique-paths/tedkimdev.go

@@ -0,0 +1,17 @@
+// TC: O(m * n)
+// SC: O(m * n)
+func uniquePaths(m int, n int) int {
+	dp := make([][]int, m+1)
+	for i := range dp {
+		dp[i] = make([]int, n+1)
+	}
+	dp[m-1][n-1] = 1
+
+	for i := m - 1; i >= 0; i-- {
+		for j := n - 1; j >= 0; j-- {
+			dp[i][j] += dp[i+1][j] + dp[i][j+1]
+		}
+	}
+
+	return dp[0][0]
+}