Stock buy and sell (DSA)

 

Problem Statement:(👈click here for GFG)

The cost of stock on each day is given in an array A[] of size N. Find all the segments of days on which you buy and sell the stock so that in between those days  for which profit can be generated

.

Note: Since there can be multiple solutions, the driver code will print 1 if your answer is correct, otherwise, it will return 0. In case there's no profit the driver code will print the string "No Profit" for a correct solution.

Example 1:

Input:
N = 7
A[] = {100,180,260,310,40,535,695}
Output:
1
Explanation:
One possible solution is (0 3) (4 6)
We can buy stock on day 0,
and sell it on 3rd day, which will 
give us maximum profit. Now, we buy 
stock on day 4 and sell it on day 6.

Example 2:

Input:
N = 5
A[] = {4,2,2,2,4}
Output:
1
Explanation:
There are multiple possible solutions.
one of them is (3 4)
We can buy stock on day 3,
and sell it on 4th day, which will 
give us maximum profit.

Your Task:
The task is to complete the function stockBuySell() which takes an array A[] and N as input parameters and finds the days of buying and selling stock. The function must return a 2D list of integers containing all the buy-sell pairs i.e. first value of pair will represent the day on which you buy the stock and second value represent the day on which you sell that stock. If there is No Profit, return an empty list.

Expected Time Complexity: O(N)
Expected Auxiliary Space: O(N)

Constraints:
2 ≤ N ≤ 10^6
0 ≤ A[i] ≤ 10^6

Solution: 

class Solution {
    //Function to find the days of buying and selling stock for max profit.
    stockBuySell(A, n)
    {
        //your code here
            let answer = [];
    let flag = false; // indicates if a buy has been made

    for (let i = 0; i < n-1; i++) {
        // find local minima
        while (i < n-1 && A[i] >= A[i+1]) {
            i++;
        }

        let buy = i;

        // find local maxima
        while (i < n-1 && A[i] <= A[i+1]) {
            i++;
        }

        let sell = i;

        if (sell > buy) {
            answer.push([buy, sell]);
            flag = true;
        }
    }

    if (!flag) {
        return [];
    } else {
        return answer;
    }
    }
}