add leetcode 54

54.spiral_matrix/main.go

@@ -0,0 +1,124 @@
+package main
+
+import "math"
+
+// brute force will result in a time limit exceeded error
+func spiralOrder(matrix [][]int) []int {
+	mixRow, mixCol := len(matrix), len(matrix[0])
+	result := make([]int, mixRow*mixCol)
+	row, col := 0, 0
+	result[0] = matrix[row][col]
+	visit := 101
+	matrix[row][col] = visit
+	direction := [][]int{{0, 1}, {1, 0}, {0, -1}, {-1, 0}}
+	for i := 1; i < len(result); {
+		for j := 0; j < len(direction); {
+			newRow, newCol := row+direction[j][0], col+direction[j][1]
+			if newRow == mixRow || newCol == mixCol ||
+				newRow < 0 || newCol < 0 {
+				j++
+				continue
+			}
+
+			if matrix[newRow][newCol] == visit {
+				j++
+				continue
+			}
+
+			row, col = newRow, newCol
+			result[i] = matrix[row][col]
+			matrix[row][col] = visit
+			i++
+			if i == len(result) {
+				break
+			}
+		}
+	}
+
+	return result
+}
+
+// optimize spiralOrder
+// time complexity: O(M * N) this is because we visit each element once.
+// space complexity: O(1)
+//
+// if we mark the cells that we visited, then when we run into a visited cell,
+// we know we need to run.
+//
+// if `changeDirection` is larger than 1, it means we are continuously
+// changing our directions, and therefore we've visited all of the elements.
+//
+// modifying the original data may not be a good choice sometimes. therefore,
+// we can also prepare another boolean matrix to store the cells we visited.
+// however, the implementation of this approach is quite similar.
+func spiralOrder2(matrix [][]int) []int {
+	m, n := len(matrix), len(matrix[0])
+	row, col := 0, 0
+	result := make([]int, 0, m*n)
+	visit := 101
+	result = append(result, matrix[row][col])
+	matrix[row][col] = visit
+
+	directions := [4][2]int{{0, 1}, {1, 0}, {0, -1}, {-1, 0}}
+	currentDirection := 0
+	changeDirection := 0
+
+	for changeDirection < 2 {
+		for row+directions[currentDirection][0] >= 0 &&
+			row+directions[currentDirection][0] < m &&
+			col+directions[currentDirection][1] >= 0 &&
+			col+directions[currentDirection][1] < n &&
+			matrix[row+directions[currentDirection][0]][col+directions[currentDirection][1]] != visit {
+			row += directions[currentDirection][0]
+			col += directions[currentDirection][1]
+			result = append(result, matrix[row][col])
+			matrix[row][col] = visit
+
+			// reset this to 0 since we did not break and change the direction
+			changeDirection = 0
+		}
+		// change our direction
+		currentDirection = (currentDirection + 1) % 4
+		// increment changeDirection because we changed our direction
+		changeDirection++
+	}
+
+	return result
+}
+
+// set up boundaries
+// time complexity: O(M * N)
+// space complexity: O(1)
+
+// there are only two movement pattern, right + down and left + up.
+// in the first case we increment either the row or column by 1, and
+// in the latter case we increment either the row or column by -1.
+// also notice that after we move horizontally the number of possible
+// vertical steps decrease by 1, and after we move vertically the number
+// of possible horizontal steps decrease by 1. when we run out of either
+// vertical steps or horizontal steps we reach the end.
+func spiralOrder3(matrix [][]int) []int {
+	m, n := len(matrix), len(matrix[0])
+	direction := 1
+	row, col := 0, -1
+	result := []int{}
+	for math.Min(float64(m), float64(n)) != 0 {
+		// move horizontally
+		for i := 0; i < n; i++ {
+			col += direction
+			result = append(result, matrix[row][col])
+		}
+		m -= 1
+
+		// move vertically
+		for i := 0; i < m; i++ {
+			row += direction
+			result = append(result, matrix[row][col])
+		}
+		n -= 1
+
+		// flip direction
+		direction *= -1
+	}
+	return result
+}

54.spiral_matrix/main_test.go

@@ -0,0 +1,64 @@
+package main
+
+import (
+	"testing"
+)
+
+func TestSpiralOrder(t *testing.T) {
+	for _, tt := range []struct {
+		matrix [][]int
+		want   []int
+	}{{
+		matrix: [][]int{{1, 2, 3}, {4, 5, 6}, {7, 8, 9}},
+		want:   []int{1, 2, 3, 6, 9, 8, 7, 4, 5},
+	}, {
+		matrix: [][]int{{1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12}},
+		want:   []int{1, 2, 3, 4, 8, 12, 11, 10, 9, 5, 6, 7},
+	}, {
+		matrix: [][]int{{8, 9, 4, 1, 2, 5}, {10, 19, 32, 14, 3, 6}},
+		want:   []int{8, 9, 4, 1, 2, 5, 6, 3, 14, 32, 19, 10},
+	}, {
+		matrix: [][]int{{-10, 0, -7}, {0, 9, -100}},
+		want:   []int{-10, 0, -7, -100, 9, 0},
+	}} {
+		matrix1 := shallowCopy2DSlice(tt.matrix)
+		got := spiralOrder(matrix1)
+		if !equal(tt.want, got) {
+			t.Errorf("got: %v, want: %v", got, tt.want)
+		}
+
+		matrix2 := shallowCopy2DSlice(tt.matrix)
+		got = spiralOrder2(matrix2)
+		if !equal(tt.want, got) {
+			t.Errorf("got: %v, want: %v", got, tt.want)
+		}
+
+		matrix3 := shallowCopy2DSlice(tt.matrix)
+		got = spiralOrder3(matrix3)
+		if !equal(tt.want, got) {
+			t.Errorf("got: %v, want: %v", got, tt.want)
+		}
+	}
+}
+
+func shallowCopy2DSlice(matrix [][]int) [][]int {
+	shallow := make([][]int, len(matrix))
+	for i := range matrix {
+		arr := make([]int, len(matrix[i]))
+		copy(arr, matrix[i])
+		shallow[i] = arr
+	}
+	return shallow
+}
+
+func equal(expect, actual []int) bool {
+	if len(expect) != len(actual) {
+		return false
+	}
+	for i := 0; i < len(expect); i++ {
+		if expect[i] != actual[i] {
+			return false
+		}
+	}
+	return true
+}

README.md

@@ -26,7 +26,8 @@
 |35|[Search Insert Position](https://leetcode.com/problems/search-insert-position)|$\color{green}{\textsf{Easy}}$|[Go]()|  
 |46|[Permutations](https://leetcode.com/problems/permutations/)|$\color{orange}{\textsf{Medium}}$|[Go](https://github.com/xxxVitoxxx/leetcode/blob/main/46.permutations/main.go)|  
 |52|[N-Queens II](https://leetcode.com/problems/n-queens-ii/)|$\color{red}{\textsf{Hard}}$|[Go](https://github.com/xxxVitoxxx/leetcode/blob/main/52.N-queens_II/main.go)|  
-|53|[Maximum Subarray](https://leetcode.com/problems/maximum-subarray)|$\color{orange}{\textsf{Medium}}$||
+|53|[Maximum Subarray](https://leetcode.com/problems/maximum-subarray)|$\color{orange}{\textsf{Medium}}$||  
+|54|[Spiral Matrix](https://leetcode.com/problems/spiral-matrix/submissions)|$\color{orange}{\textsf{Medium}}$|[Go](https://github.com/xxxVitoxxx/leetcode/blob/main/54.spiral_matrix/main.go)|  
 |58|[Length of Last Word](https://leetcode.com/problems/length-of-last-word)|$\color{green}{\textsf{Easy}}$||
 |61|[Rotate List](https://leetcode.com/problems/rotate-list)|$\color{orange}{\textsf{Medium}}$|[Go](https://github.com/xxxVitoxxx/leetcode/blob/main/61.rotate_list/main.go)|
 |66|[Plus One](https://leetcode.com/problems/plus-one)|$\color{green}{\textsf{Easy}}$||