Previous Smaller Element | Nearest Smaller Element | Techie Delight | Interview Bit

 Previous Smaller Element | Techie Delight

Given an integer array, find the previous smaller element for every array element. The previous smaller element of a number `x` is the first smaller number to the left of `x` in the array.

In other words, for each element A[i] in the array A, find an element A[j] such that j < i and A[j] < A[i] and value of j should be as maximum as possible. If the previous smaller element doesn't in the array for any element, consider it -1.

Input : [2, 5, 3, 7, 8, 1, 9]

Output: [-1, 2, 2, 3, 7, -1, 1]

Input : [5, 7, 4, 9, 8, 10]

Output: [-1, 5, -1, 4, 4, 8]

Note that the first element always has a previous smaller element as -1.

Interview Bit

Given an array, find the nearest smaller element G[i] for every element A[i] in the array such that the element has an index smaller than i.

More formally,

    G[i] for an element A[i] = an element A[j] such that 
    j is maximum possible AND 
    j < i AND
    A[j] < A[i]

Elements for which no smaller element exist, consider next smaller element as -1.

Input Format

The only argument given is integer array A.

Output Format

Return the integar array G such that G[i] contains nearest smaller number than A[i].If no such element occurs G[i] should be -1.

For Example

Input 1:
    A = [4, 5, 2, 10, 8]
Output 1:
    G = [-1, 4, -1, 2, 2]
Explaination 1:
    index 1: No element less than 4 in left of 4, G[1] = -1
    index 2: A[1] is only element less than A[2], G[2] = A[1]
    index 3: No element less than 2 in left of 2, G[3] = -1
    index 4: A[3] is nearest element which is less than A[4], G[4] = A[3]
    index 4: A[3] is nearest element which is less than A[5], G[5] = A[3]
    
Input 2:
    A = [3, 2, 1]
Output 2:
    [-1, -1, -1]
Explaination 2:
    index 1: No element less than 3 in left of 3, G[1] = -1
    index 2: No element less than 2 in left of 2, G[2] = -1
    index 3: No element less than 1 in left of 1, G[3] = -1