（Array）27. Remove Element

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 in place with constant memory.

The order of elements can be changed. It doesn't matter what you leave beyond the new length.

Example:
Given input array nums = [3,2,2,3], val = 3

Your function should return length = 2, with the first two elements of nums being 2.

public class Solution {
  public int removeElement(int[] nums, int val) {   //更好的方法是设置两个指针都是从0开始，这样直接return i了
		int i = 0;
		int j = nums.length - 1;
		while(j > i) {
			while (nums[i] != val && j>i)  //注意这个条件
				i++;
			while (nums[j] == val && j>i)
				j--;
			swap(nums, i++, j--);
		}
		int res = 0;
		for (i = 0; i < nums.length; i++) {
			//System.out.print(nums[i] + " ");
			if (nums[i] != val)
				res++;
		}
		return res;

	}

	public  void swap(int[] arr, int i, int j) {
		int temp = arr[i];
		arr[i] = arr[j];
		arr[j] = temp;
	}
}