Given an array and a value, remove all instances of that value in-place and return the new length.
Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.
The order of elements can be changed. It doesn't matter what you leave beyond the new length.
翻译：给定一个数组和一个值，移除数组中为该值的元素，返回新的数组长度。（其实是原数组的长度减去特定值个数）
但是不能占用额外的空间来另声明一个数组，必须在O(1)的内存占用中做完。
元素的顺序可以更改~新数组尾部是什么不重要。
Example:
Given nums = [3,2,2,3], val = 3, Your function should return length = 2, with the first two elements of nums being 2.
答案
class Solution {
public int removeElement(int[] nums, int val) {
if (nums.length==0) return 0; //特殊情况
int j=0;
for (int i=0;i<nums.length;i++){
if (nums[i]!=val){//和给定值不相等就留下
nums[j]=nums[i];
j++;
}
}
return j;
}
}