0096_med_unique_binary_search_tree.js

var numTrees = function(n) {
  let dp = new Array(n+1).fill(0);
  dp[0] = 1;
  for (let i = 1; i <= n; i++) {
    for (let j = 1; j <= i; j++) {
      dp[i] += dp[j-1] * dp[i-j];
    }
  }
  return dp[n];
};
numTrees(7)