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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];
}
