題目

You are given an integer array nums of length n where nums is a permutation of the numbers in the range [0, n - 1].

You should build a set s[k] = {nums[k], nums[nums[k]], nums[nums[nums[k]]], ... } subjected to the following rule:

• The first element in s[k] starts with the selection of the element nums[k] of index = k.
• The next element in s[k] should be nums[nums[k]], and then nums[nums[nums[k]]], and so on.
• We stop adding right before a duplicate element occurs in s[k].

Return the longest length of a set s[k].

Example 1:

Input: nums = [5,4,0,3,1,6,2]
Output: 4
Explanation: 
nums[0] = 5, nums[1] = 4, nums[2] = 0, nums[3] = 3, nums[4] = 1, nums[5] = 6, nums[6] = 2.
One of the longest sets s[k]:
s[0] = {nums[0], nums[5], nums[6], nums[2]} = {5, 6, 2, 0}

Example 2:

Input: nums = [0,1,2]
Output: 1

Constraints:

• 1 <= nums.length <= 105
• 0 <= nums[i] < nums.length
• All the values of nums are unique.

解題

class Solution {

    /**
     * @param Integer[] $nums
     * @return Integer
     */
    function arrayNesting($nums) {
        
        $result = 0;
        
        foreach($nums as $key => $val) {
            if (array_key_exists($key, $nums)) {
                $k = $nums[$key];
                unset($nums[$key]);
                $count = 1;
                
                while(array_key_exists($k, $nums)) {
                    $k = $nums[$k];
                    $count++;
                }
                
                $result = max($result, $count);
            }
        }
        
        return $result;
    }
}

Runtime: 127 ms, faster than 9.09% of PHP online submissions for Array Nesting.

Memory Usage: 18.4 MB, less than 77.27% of PHP online submissions for Array Nesting.

進階

/**
 * @param Integer[] $nums
 * @return Integer
 */
function arrayNesting($nums) {

    $result = 0;
    for ($i = 0; $i < count($nums); ++$i) {
        if ($nums[$i] != -1) {
            $count = 0;
            while($nums[$i] != -1) {
                $j = $nums[$i];
                $nums[$i] = -1;
                $i = $j;
                $count++;
            }
            $result = max($result, $count);
        }
    }

    return $result;
}

Runtime: 40 ms, faster than 79.17% of PHP online submissions for Array Nesting.

Memory Usage: 18.5 MB, less than 25.00% of PHP online submissions for Array Nesting.

LeetCode 565. Array Nesting (PHP)
Bebe

今天刷了兩題，有夠上進～值得吃薯條慶祝！

題目

Given an integer array nums, move all 0‘s to the end of it while maintaining the relative order of the non-zero elements.

Note that you must do this in-place without making a copy of the array.

Example 1:

Input: nums = [0,1,0,3,12]
Output: [1,3,12,0,0]

Example 2:

Input: nums = [0]
Output: [0]

Constraints:

• 1 <= nums.length <= 104
• -231 <= nums[i] <= 231 - 1

Follow up: Could you minimize the total number of operations done?

解題

這題很簡單，自信心＋＋
將給定陣列的0往最後面放即可～

我是先將值為零的元素從陣列刪除，然後計數器加一，再跑一次迴圈把零補上。
不過後來想到，刪掉時同時補上也行，就不用再多一個while迴圈了。

class Solution {

    /**
     * @param Integer[] $nums
     * @return NULL
     */
    function moveZeroes(&$nums) {
        $i = 0;
        foreach($nums as $key => $val) {
            if($nums[$key] == 0) {
                unset($nums[$key]);
                $i++;
            }
        }
                    
        while($i > 0) {
            $nums[] = 0;
            $i--;
        }
    }
}

Runtime: 12 ms, faster than 81.89% of PHP online submissions for Move Zeroes.

Memory Usage: 17 MB, less than 25.20% of PHP online submissions for Move Zeroes.

LeetCode 283. Move Zeroes (PHP)
Bebe

不知道吃錯什麼藥，突然上進了起來，竟然來刷題！目前程度很普通，先挑Easy的來增加自信(/ω＼)

題目

Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

You can return the answer in any order.

Example 1:

Input: nums = [2,7,11,15], target = 9
Output: [0,1]
Output: Because nums[0] + nums[1] == 9, we return [0, 1].

Example 2:

Input: nums = [3,2,4], target = 6
Output: [1,2]

Example 3:

Input: nums = [3,3], target = 6
Output: [0,1]

Constraints:

• 2 <= nums.length <= 104
• -109 <= nums[i] <= 109
• -109 <= target <= 109
• Only one valid answer exists.

Follow-up: Can you come up with an algorithm that is less than O(n2) time complexity?

解題

這題我直接用暴力解法 (/ω＼)

題目很好懂，給訂一個陣列，找出不重複的兩個值，相加等於給定值。

class Solution {

    /**
     * @param Integer[] $nums
     * @param Integer $target
     * @return Integer[]
     */
    function twoSum($nums, $target) {
        $cal = [];
        foreach ($nums as $key1 => $val1) {
            foreach ($nums as $key2 => $val2) {
                if ($key1 == $key2) continue;
                else if($target - $val1 == $val2) {
                    $cal[] = $key1;
                    $cal[] = $key2;
                    break 2;
                }
            }
        }
        
        return $cal;
    }
}

Runtime: 2335 ms, faster than 14.53% of PHP online submissions for Two Sum.

Memory Usage: 16.2 MB, less than 97.47% of PHP online submissions for Two Sum.

進階

果然跑兩個迴圈執行時間會很久，參考網路上大神寫的，執行速度差超級多！又長知識了

class Solution {

    /**
     * @param Integer[] $nums
     * @param Integer $target
     * @return Integer[]
     */
    function twoSum($nums, $target) {
        foreach ($nums as $key => $val) {
            unset($nums[$key]);
            $nextKey = array_search(($target - $val), $nums);
            if ($nextKey) {
                return [$key, $nextKey];
            }
        }
        return [];
    }
}

Runtime: 270 ms, faster than 56.82% of PHP online submissions for Two Sum.

Memory Usage: 16.2 MB, less than 97.47% of PHP online submissions for Two Sum.

看到才56.82%不死心，又繼續測試了一下！！有差有差

class Solution {

    /**
     * @param Integer[] $nums
     * @param Integer $target
     * @return Integer[]
     */
    function twoSum($nums, $target) {
        $map = [];
        for ($i=0;$i<=count($nums);$i++) {
            $diff = $target - $nums[$i];

            if (array_key_exists($diff, $map)) {
                return [$map[$diff], $i];
            } else {
                $map[$nums[$i]] = $i;
            }
        }
        return [];
    }
}

Runtime: 28 ms, faster than 70.92% of PHP online submissions for Two Sum.

Memory Usage: 16.6 MB, less than 27.48% of PHP online submissions for Two Sum.

LeetCode 1. Two Sum (PHP)
Bebe