Counting Valleys - ReasonML

counting-valleys.re

let countingValleys = (~s) => {
  let rec iter = (~numberOfValleys, ~level, ~s) =>
    if (String.length(s) === 0) {
      numberOfValleys;
    } else {
      let next = s.[0];
      let rest = String.sub(s, 1, String.length(s) - 1);
      switch (next, level) {
      | ('U', (-1)) => iter(~numberOfValleys=numberOfValleys + 1, ~level=level + 1, ~s=rest)
      | ('U', _) => iter(~numberOfValleys, ~level=level + 1, ~s=rest)
      | ('D', _) => iter(~numberOfValleys, ~level=level - 1, ~s=rest)
      | (_, _) => iter(~numberOfValleys, ~level, ~s=rest)
      };
    };
  iter(~s, ~numberOfValleys=0, ~level=0);
};