Function numDistinct

javascript/0115-distinct-subsequences.js:10–30

(s, t, i = 0, j = 0, memo = initMemo(s, t))

 * @return {number}
 */
var numDistinct = (s, t, i = 0, j = 0, memo = initMemo(s, t)) => {
    const isBaseCase1 = s.length < t.length;
    if (isBaseCase1) return 0;

    const isBaseCase2 = j === t.length;
    if (isBaseCase2) return 1;

    const isBaseCase3 = i === s.length;
    if (isBaseCase3) return 0;

    const hasSeen = memo[i][j] !== null;
    if (hasSeen) return memo[i][j];

    return dfs(
        s,
        t,
        i,
        j,
        memo,
    ); /* Time O(N * M) | Space O((N * M) + HEIGHT) */
};

var initMemo = (s, t) =>
    new Array(s.length).fill().map(() => new Array(t.length).fill(null));