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// arr 已知一些数数组（正序） num缺失的第几个数
function findMissNum(arr, num) {
  let missArr = [];
  let len = arr.length;
  let max = arr[len - 1];
  for (let i = 1; i <= max; i++) {
    if (!arr.includes(i)) {
      missArr.push(i);
    }
  }
  let missArrLen = missArr.length;
  if (num > missArrLen) {
    return (missArr.length ? missArr[missArrLen - 1] : max) + num - missArrLen;
  }
  return missArr[num - 1];
}