Remove Element

Given an array and a value, remove all instances of that value in place and return the new length.

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

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如果用erase 耗时比较长，题目说了不要管新长度n之后的内容了，那就不删除，放在n后面

class Solution {
public:
    int removeElement(vector<int>& nums, int val) {
        int l = 0;
        int r = nums.size()-1;
       //将val移动到最后
        while (l <= r) {
            while (l <= r && nums[r] == val) {
                r--;
            }
            while (l <= r && nums[l] != val) {
                l++;
            }
            if (l <= r) {
                nums[l] = nums[r];
                nums[r] = val;
                r--;
                l++;
            }
        }
        return r+1;
    }
};