LeetCode 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.

Clarification:

Confused why the returned value is an integer but your answer is an array?

Note that the input array is passed in by reference, which means modification to the input array will be known to the caller as well.

Internally you can think of this:

// nums is passed in by reference. (i.e., without making a copy)
int len = removeElement(nums, val);

// any modification to nums in your function would be known by the caller.
// using the length returned by your function, it prints the first len elements.
for (int i = 0; i < len; i++) {
    print(nums[i]);
}

初看该题，简单，传入数组去掉重复的数字，其它数字的个数，感叹为何如此简单

package com.lihuia.leetcode27;

/**
 * Copyright (C), lihuia.com
 * FileName: Solution
 * Author:   lihui
 * Date:     2018/7/23
 */

public class Solution {

    public int removeElement(int[] nums, int val) {
        int maxLen = nums.length;
        if (maxLen == 0) {
            return 0;
        }
        int len = 0;
        for (int i = 0; i < maxLen; i++) {
            if (nums[i] != val) {
                len++;
            }
        }
        return len;
    }
}

结果居然报错了，testcase是传入[3,2,2,3]，删除3，期望是[2,2]，但是返回了[3,2]

仔细看了下题目，才发现，最后还要求

Internally you can think of this:

// nums is passed in by reference. (i.e., without making a copy)
int len = removeElement(nums, val);

// any modification to nums in your function would be known by the caller.
// using the length returned by your function, it prints the first len elements.
for (int i = 0; i < len; i++) {
    print(nums[i]);
}

不光要求返回len，而且要求nums是删除了val元素后的剩余数组

那就和上一道一样，和val不同的数字就付给另一个下标

package com.lihuia.leetcode27;

/**
 * Copyright (C), lihuia.com
 * FileName: Solution
 * Author:   lihui
 * Date:     2018/7/23
 */

public class Solution {

    public int removeElement(int[] nums, int val) {
        int maxLen = nums.length;
        if (maxLen == 0) {
            return 0;
        }
        int len = 0;
        for (int i = 0; i < maxLen; i++) {
            if (nums[i] != val) {
                nums[len++] = nums[i];
            }
        }
        return len;
    }
}

传一个值，len就+1，len正好就是长度