从数组中选择一个随机元素，重复直到满足条件

Question

I have the following issue: I have a fixed sum [30] and array of numbers. My questions is how do I subtract random numbers of num from sum until i get the rest number >1, <2 like 1.09 or 1.05?

var num= [0.99, 1.99, 2.99, 3.99, 4.99, 5.99, 6.99, 7.99, 8.99, 9.99];
var sum= [30];

---

console.log()

[30]

[0.99,
1.99,
0.99,
4.99,
6.99,
1.99,
2.99,
4.99
2.99]

[1.09]

---

console.log(again)

[30]

[7.99,
6.99,
4.99,
6.99,
1.99,

[1.05]

Answer 1

You need to use 0/1 knapsack dynamic programming here. It is standard knapsack problem.

Suppose, you are trying in first number. You may either subtract this number from sum or ignore this number. So you will try all possibilities. This kind of taking/non-taking is called 0/1 knapsack.

You can learn 0/1 knapsack from this link: https://www.geeksforgeeks.org/0-1-knapsack-problem-dp-10/

Answer 2

The function expects you to give it a target sum (as a number, not array with 1 element), the array of possible subtraction values and a target array of 2 elements - min and max.

 var num = [0.99, 1.99, 2.99, 3.99, 4.99, 5.99, 6.99, 7.99, 8.99, 9.99]; var sum = 30; var target = [1, 2]; function subtract(sum, num, target) { // pick a random index of whatever array is provided. const randomIndex = Math.round((num.length - 1) * Math.random()); // * 100 / 100 is to successfully round to the 2nd decimal place. const newSum = Math.round((sum - num[randomIndex]) * 100) / 100; if (newSum >= target[1]) { console.log(`Subtracted ${num[randomIndex]}. Result is ${newSum}.`); subtract(newSum, num, target); } else if (newSum > target[0] && newSum <= target[1]) { console.log(`Subtracted ${num[randomIndex]}. Result is ${newSum}. Done.`); } else { console.log(`Couldn't subtract ${num[randomIndex]}. Result is ${sum}.`); subtract(sum, num, target); } } subtract(sum, num, target);