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+## Make the Deadfish swim
+
+Write a simple parser that will parse and run Deadfish.
+
+Deadfish has 4 commands, each 1 character long:
+
+- `i` increments the value (initially 0)
+- `d` decrements the value
+- `s` squares the value
+- `o` outputs the value into the return array
+
+Invalid characters should be ignored.
+
+```rust
+parse("iiisdoso") => [ 8, 64 ]
+```