JS求组合数

获取从[0, 1, 2, ... , m]闭区间的数中任选m个数，求其组合和组合的个数，即

[C_n^m ]

// 获取[1, end]闭区间的组合数
function getCombine(end, num) {
  if (num > end + 1 || num === 0) {
    return []
  }
  let set = new Set()

  f(num)

  /**
   *
   * @param round 要循环几层
   * @param arr
   */
  function f(round, arr = []) {
    if (round === 0) return
    for (let i = 1; i <= end; i++) {
      if (round === 1) { // 最内层的循环
        let result = [...arr, i]
        if (isSet(result)) {
          result = result.sort()
          result = result.join(' ')
          set.add(result)
        }
      }
      f(round - 1, [...arr, i])
    }
  }

  return Array.from(set)
}


function isSet(arr) {
  return new Set(arr).size === arr.length
}
// no-log

// log
let c1 = getCombine(6, 4)
console.log(c1)

let c2 = getCombine(10,3)
console.log(c2.length)