leetcode 1269

leetcode/1269/1269.go

@@ -0,0 +1,32 @@
+const mod = 1e9+7
+
+func min(a, b int) int {
+    if a < b {
+        return a
+    }
+    return b
+}
+
+func numWays(steps int, arrLen int) int {
+    n := min(steps / 2 + 1, arrLen)
+    
+    cur := make([]int, n)
+    cur[0] = 1
+    for i := 0; i < steps; i++ {
+        nxt := make([]int, n)
+        for j := 0; j < n; j++ {
+            if cur[j] > 0 {
+                if j - 1 >= 0 {
+                    nxt[j-1] = (nxt[j-1] + cur[j]) % mod
+                }
+                nxt[j] = (nxt[j] + cur[j]) % mod
+                if j + 1 < n {
+                    nxt[j+1] = (nxt[j+1] + cur[j]) % mod
+                }
+            }
+        }
+        cur = nxt
+        // fmt.Println(cur)
+    }
+    return cur[0] % mod
+}