027_Remove_Element.md

27. Remove Element

---

Description

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.

Javascript

思路：splice库函数解决数组自身切割问题。

/**
 * @param {number[]} nums
 * @param {number} val
 * @return {number}
 */
var removeElement = function(nums, val) {
    var l = nums.length;
    for (var i = 0; i < l; i++) {
        if (nums[i] === val) {
            nums.splice(i, 1);
            i--;
        }
    }
    return nums.length;
};

Java

解法一：双指针。

public class Solution {
    public int removeElement(int[] nums, int val) {
        int i = 0, j = nums.length - 1, cnt = 0;
        while (i < j) {
            while (nums[i] != val && i < j) {
                i++;
            }
            int tmp = nums[i];
            nums[i] = nums[j];
            nums[j] = tmp;
            j--;
        }
        j = nums.length - 1;
        while (j >= 0 && nums[j] == val) {
            cnt++;
            j--;
        }
        return nums.length - cnt;
    }
}

解法二：单指针覆盖法。

public class Solution {
    int removeElement(int A[], int elem) {
        int begin = 0;
        for(int i = 0;i < A.length; i++) {
            if(A[i] != elem) {
                A[begin++] = A[i];
            }
        }
        return begin;
    }
}