Title

the problem link

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.

Example:

Given nums = [3,2,2,3], val = 3,

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

删除一个元素，不能用其他内容，方法1是两个指针，方法二是交换

Solution

//cpp:
class Solution {
public:
	int removeElement(vector<int>& nums, int val) {
		int i = 0;
		for (int j = 0; j < nums.size(); j++) {
			if (nums[j] != val) {
				nums[i] = nums[j];
				i++;
			}
		}
		return i;
	}
};

OR

class Solution {
public:
	int removeElement(vector<int>& nums, int val) {
		int n = nums.size();
		int i = 0;
		while (i < n) {
			if (nums[i] == val) {
				nums[i] = nums[n - 1];
				n--;
			}
			else
				i++;
		}
		return n;
	}
};