先排后找可以让结果更简单

int cmp(const void* a, const void* b){return *(int*)a - *(int*)b;
}
int missingNumber(int* nums, int numsSize){qsort(nums, numsSize, 4, cmp);for(int i=0; i<numsSize; ++i){if(nums[i] == i){continue;}else{return i;}}return numsSize;
}