删除等于n的数，并返回剩余元素个数
Given nums = [3,2,2,3], val = 3, Your function should return length = 2, with the first two elements of nums being 2.
class Solution { public: int removeElement(vector<int>& nums, int val) { int count = 0; int len = nums.size(); for (int i=0;i<len;i++){ if (nums[i]!=val){ nums[count++] = nums[i]; } } return count; } };