add: Unique Paths

UniquePaths/step1.md

@@ -0,0 +1,27 @@
+```go
+// Use DP
+// When x == 0 or y == 0 the number of path will be 1
+// Other than that, the number of path will be dp[y][x - 1] + dp[y - 1][x]
+// Time complexity: O(M * n)
+// Space complexity: O(M * N)
+// Time spend: 03:14
+package main
+func uniquePaths(m int, n int) int {
+    dp := make([][]int, m)
+    for i := range dp {
+        dp[i] = make([]int, n)
+    }
+
+    for y := range dp {
+        for x := range dp[y] {
+            if x == 0 || y == 0 {
+                dp[y][x] = 1
+                continue
+            }
+            dp[y][x] = dp[y - 1][x] + dp[y][x - 1]
+        }
+    }
+
+    return dp[m - 1][n - 1]
+}
+```

UniquePaths/step2.md

@@ -0,0 +1,22 @@
+```go
+// Time spend: 01:07
+package main
+func uniquePaths(m int, n int) int {
+    dp := make([][]int, m)
+    for i := range dp {
+        dp[i] = make([]int, n)
+    }
+
+    for y := range dp {
+        for x := range dp[y] {
+            if x == 0 || y == 0 {
+                dp[y][x] = 1
+                continue
+            }
+            dp[y][x] = dp[y - 1][x] + dp[y][x - 1]
+        }
+    }
+
+    return dp[m - 1][n - 1]
+}
+```

UniquePaths/step3.md

@@ -0,0 +1,68 @@
+```go
+// Time spend: 01:12
+package main
+func uniquePaths(m int, n int) int {
+    dp := make([][]int, m)
+    for i := range dp {
+        dp[i] = make([]int, n)
+    }
+
+    for y := range dp {
+        for x := range dp[y] {
+            if x == 0 || y == 0 {
+                dp[y][x] = 1
+                continue
+            }
+            dp[y][x] = dp[y - 1][x] + dp[y][x - 1]
+        }
+    }
+
+    return dp[m - 1][n - 1]
+}
+```
+
+```go
+// Time spend: 01:06
+package main
+func uniquePaths(m int, n int) int {
+    dp := make([][]int, m)
+    for i := range dp {
+        dp[i] = make([]int, n)
+    }
+
+    for y := range dp {
+        for x := range dp[y] {
+            if x == 0 || y == 0 {
+                dp[y][x] = 1
+                continue
+            }
+            dp[y][x] = dp[y - 1][x] + dp[y][x - 1]
+        }
+    }
+
+    return dp[m - 1][n - 1]
+}
+```
+
+```go
+// Time spend: 01:08
+package main
+func uniquePaths(m int, n int) int {
+    dp := make([][]int, m)
+    for i := range dp {
+        dp[i] = make([]int, n)
+    }
+
+    for y := range dp {
+        for x := range dp[y] {
+            if x == 0 || y == 0 {
+                dp[y][x] = 1
+                continue
+            }
+            dp[y][x] = dp[y - 1][x] + dp[y][x - 1]
+        }
+    }
+
+    return dp[m - 1][n - 1]
+}
+```