【leetcode】27. Remove Element 刪除陣列指定值的元素

1. 題目

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.

2. 思路

遍歷，遇到待刪除的元素，將當前的末尾移到當前位置，繼續處理當前位置。
當前末尾也可以持續前進直到遇到不是待刪除元素，或者是全部處理完了。

3. 程式碼

耗時：3ms

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