27. Remove Element
Given an array nums and a value val, 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 1:
Given nums = [3,2,2,3], val = 3,
Your function should return length = 2, with the first two elements of nums being 2.
It doesn't matter what you leave beyond the returned length.
Example 2:
Given nums = [0,1,2,2,3,0,4,2], val = 2,
Your function should return length = 5, with the first five elements of nums containing 0, 1, 3, 0, and 4.
Note that the order of those five elements can be arbitrary.
It doesn't matter what values are set beyond the returned length.
難度：easy
題目：
給定整數陣列和一個特定值，原地移除所有給定的特定值例項，並且返回新陣列長度。
不要申請額外的空間，必須在給出的陣列上原地改動。
陣列元素所在位置可以被改動。陣列實際長度可以超過新陣列長度。
思路：從後向前轉換
Runtime: 4 ms, faster than 100.00% of Java online submissions for Remove Element.
Memory Usage: 26.9 MB, less than 13.46% of Java online submissions for Remove Element.
class Solution {
public int removeElement(int[] nums, int val) {
int idx = nums.length - 1;
for (int i = 0; i <= idx; i++) {
if (nums[i] == val) {
if (nums[i] == nums[idx]) {
i--;
} else {
nums[i] = nums[idx];
}
idx--;
}
}
return idx + 1;
}
}