feat(uniquepaths): add solution for unique paths problem (#716)

* feat(uniquepaths): add solution for unique paths problem

* fix: Remove extra unused memory

Author: rares985

dynamic/uniquepaths.go

@@ -0,0 +1,31 @@
+// See https://leetcode.com/problems/unique-paths/
+// author: Rares Mateizer (https://github.com/rares985)
+package dynamic
+
+// UniquePaths implements the solution to the "Unique Paths" problem
+func UniquePaths(m, n int) int {
+	if m <= 0 || n <= 0 {
+		return 0
+	}
+
+	grid := make([][]int, m)
+	for i := range grid {
+		grid[i] = make([]int, n)
+	}
+
+	for i := 0; i < m; i++ {
+		grid[i][0] = 1
+	}
+
+	for j := 0; j < n; j++ {
+		grid[0][j] = 1
+	}
+
+	for i := 1; i < m; i++ {
+		for j := 1; j < n; j++ {
+			grid[i][j] = grid[i-1][j] + grid[i][j-1]
+		}
+	}
+
+	return grid[m-1][n-1]
+}

dynamic/uniquepaths_test.go

@@ -0,0 +1,28 @@
+package dynamic
+
+import (
+	"testing"
+)
+
+func TestUniquePaths(t *testing.T) {
+	testCases := map[string]struct {
+		m    int
+		n    int
+		want int
+	}{
+		"negative sizes":               {-1, -1, 0},
+		"empty matrix both dimensions": {0, 0, 0},
+		"empty matrix one dimension":   {0, 1, 0},
+		"one element":                  {1, 1, 1},
+		"small matrix":                 {2, 2, 2},
+		"stress test":                  {1000, 1000, 2874513998398909184},
+	}
+
+	for name, test := range testCases {
+		t.Run(name, func(t *testing.T) {
+			if got := UniquePaths(test.m, test.n); got != test.want {
+				t.Errorf("UniquePaths(%v, %v) = %v, want %v", test.m, test.n, got, test.want)
+			}
+		})
+	}
+}