day10.java

problem 1 : https://leetcode.com/problems/rearrange-array-elements-by-sign/description/

class Solution {
    public int[] rearrangeArray(int[] nums) {
        int n=nums.length,k=0,j=0;
        int s=n/2;
        int []pos=new int[s];
        int []neg=new int[s];
        for(int i=0;i<n;i++){
            if(nums[i]>=0){
                pos[k]=nums[i];
                k++;
            }
            else{
                neg[j]=nums[i];
                j++;
            }
        }
        k=0;
        j=0;
        for(int i=0;i<n;i++){
            if(i%2==0){
                nums[i]=pos[k];
                k++;
            }
            else{
                nums[i]=neg[j];
                j++;
            }
        }
        return nums;
    }
}
TC:O(n)
SC:O(1)
Approach:we will make two seperate array for positive and for negative the add one by one to original array

problem 2:
import java.util.*;

class Solution {
    public void nextPermutation(int[] nums) {
        int n = nums.length; 
        int ind = -1; 
        
        for (int i = n - 2; i >= 0; i--) {
            if (nums[i] < nums[i + 1]) {
                ind = i;
                break;
            }
        }

        if (ind == -1) {
            reverse(nums, 0, n - 1);
            return;
        }

        for (int i = n - 1; i > ind; i--) {
            if (nums[i] > nums[ind]) {
                int tmp = nums[i];
                nums[i] = nums[ind];
                nums[ind] = tmp;
                break;
            }
        }

        reverse(nums, ind + 1, n - 1);
    }

    private void reverse(int[] nums, int start, int end) {
        while (start < end) {
            int tmp = nums[start];
            nums[start] = nums[end];
            nums[end] = tmp;
            start++;
            end--;
        }
    }
}
TC-O(n)
SC-O(1)
    
problem 3: https://leetcode.com/problems/best-time-to-buy-and-sell-stock/description/ 
class Solution {
    public int maxProfit(int[] prices) {
        int minPrice = Integer.MAX_VALUE;
        int maxProfit = 0;
        for (int price : prices) {
            if (price < minPrice) {
                minPrice = price; 
            } else if (price - minPrice > maxProfit) {
                maxProfit = price - minPrice; 
            }
        }
        return maxProfit;
    }
}
TC:-O(n)
SC:-O(1)