[LeetCode] Algorithm I - Day 2 Two Pointers

Algorithm I - Day 2 Two Pointers

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977. Squares of a Sorted Array

Given an integer array nums sorted in non-decreasing order, return an array of the squares of each number sorted in non-decreasing order.

 

Example 1:

Input: nums = [-4,-1,0,3,10]
Output: [0,1,9,16,100]
Explanation: After squaring, the array becomes [16,1,0,9,100].
After sorting, it becomes [0,1,9,16,100].

Example 2:

Input: nums = [-7,-3,2,3,11]
Output: [4,9,9,49,121]

 

Constraints:

• 1 <= nums.length <= 104
• -104 <= nums[i] <= 104
• nums is sorted in non-decreasing order.

 

 

📖 문제. 해당 배열의 제곱값을 오름차순으로 정렬하시오.

class Solution {
    public int[] sortedSquares(int[] nums) {
        for(int i=0; i<nums.length; i++){
            nums[i] *= nums[i];
        }
        Arrays.sort(nums);
        return nums;
    }
}

JAVA SOLUTION CODE 👍

class Solution {
    public int[] sortedSquares(int[] A) {
        int n = A.length;
        int[] result = new int[n];
        //we have positive end of the numberline and negative end
        //which ever end's absolute value is larger then it is the bigger one
        int i = 0, j = n - 1;
        for (int p = n - 1; p >= 0; p--) {
            if (Math.abs(A[i]) > Math.abs(A[j])) {
                result[p] = A[i] * A[i];
                i++;
            } else {
                result[p] = A[j] * A[j];
                j--;
            }
        }
        return result;
    }
}

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189. Rotate Array

Given an array, rotate the array to the right by k steps, where k is non-negative.

Example 1:

Input: nums = [1,2,3,4,5,6,7], k = 3
Output: [5,6,7,1,2,3,4]
Explanation:
rotate 1 steps to the right: [7,1,2,3,4,5,6]
rotate 2 steps to the right: [6,7,1,2,3,4,5]
rotate 3 steps to the right: [5,6,7,1,2,3,4]

Example 2:

Input: nums = [-1,-100,3,99], k = 2
Output: [3,99,-1,-100]
Explanation: 
rotate 1 steps to the right: [99,-1,-100,3]
rotate 2 steps to the right: [3,99,-1,-100]

 

Constraints:

• 1 <= nums.length <= 105
• -231 <= nums[i] <= 231 - 1
• 0 <= k <= 105

📖 문제. 배열을 오른쪽으로 k단계씩 회전하시오.

class Solution {
    public void rotate(int[] nums, int k) {
        
        int[] answer = new int[nums.length];
        for(int i=0; i<nums.length; i++){
            answer[(i+k)%nums.length] = nums[i]; 
        }
        for(int i=0; i<nums.length; i++){
            nums[i] = answer[i];
        }      
    }
}