ds-algo-study/DS-n-Algos/ALGO/tabulation_project/lib/problems.js

Just experimenting with publishing a package

// Write a function, lucasNumberMemo(n), that takes in a number.
// The function should return the n-th number of the Lucas Sequence.
// The 0-th number of the Lucas Sequence is 2.
// The 1-st number of the Lucas Sequence is 1
// To generate the next number of the sequence, we add up the previous two numbers.
//
// For example, the sequence begins: 2, 1, 3, 4, 7, 11, ...
//
// Solve this recursively with memoization.
//
// Examples:
//
// lucasNumberMemo(0)   // => 2
// lucasNumberMemo(1)   // => 1
// lucasNumberMemo(40)  // => 228826127
// lucasNumberMemo(41)  // => 370248451
// lucasNumberMemo(42)  // => 599074578
function lucasNumberMemo(n, memo = {}) {
  if (n in memo) return memo[n];
  if (n === 0) return 2;
  if (n === 1) return 1;
  memo[n] = lucasNumberMemo(n - 1, memo) + lucasNumberMemo(n - 2, memo);
  return memo[n];
}

// Write a function, minChange(coins, amount), that accepts an array of coin values
// and a target amount as arguments. The method should the minimum number of coins needed
// to make the target amount. A coin value can be used multiple times.
//
// After you pass the first 3 examples, you'll likely need to memoize your code
// in order to pass the 4th example in a decent runtime.
//
// Examples:
//
// minChange([1, 2, 5], 11)         // => 3, because 5 + 5 + 1 = 11
// minChange([1, 4, 5], 8))         // => 2, because 4 + 4 = 8
// minChange([1, 5, 10, 25], 15)    // => 2, because 10 + 5 = 15
// minChange([1, 5, 10, 25], 100)   // => 4, because 25 + 25 + 25 + 25 = 100
function minChange(coins, amount, memo = {}) {
  if (amount in memo) return memo[amount];
  if (amount === 0) return 0;
  let numCoins = [];
  coins.forEach(coin => {
    if (coin <= amount) {
      numCoins.push(minChange(coins, amount - coin, memo) + 1);
    }
  });
  memo[amount] = Math.min(...numCoins);
  return memo[amount];
}

module.exports = {
  lucasNumberMemo,
  minChange
};