function arrayPreviousLess(nums) {
    //  write code here.
    let stack = []
    let result = []
    nums.map((num, i) => {
        while(stack.length > 0 && stack[stack.length-1] > num)
            stack.pop()
        if(stack.length == 0){
            result.push(-1)
            stack.push(num)
        }
        else{
            result.push(stack[stack.length-1])
            stack.push(num)
        }
    })
    return result
}



/**
* Test Suite 
*/
describe('arrayPreviousLess()', () => {
    it('shift previous postions from the left to a smaller value or store -1', () => {
        // arrange
        const nums = [3, 5, 2, 4, 5];
        
        // act
        const result = arrayPreviousLess(nums);

        // log
        console.log("result: ", result);
        
        // assert
        expect(result).toEqual([-1, 3, -1, 2, 4]);
    });
    
    it('shift previous postions from the left to a smaller value or store -1', () => {
        // arrange
        const nums = [3, 4, 5, 2, 1, 4, 5];
        
        // act
        const result = arrayPreviousLess(nums);

        // log
        console.log("result: ", result);
        
        // assert
        expect(result).toEqual([-1, 3, 4, -1, -1, 1, 4]);
    });
    
    it('shift previous postions from the left to a smaller value or store -1', () => {
        // arrange
        const nums = [5, 4, 3, 2, 1];
        
        // act
        const result = arrayPreviousLess(nums);

        // log
        console.log("result: ", result);
        
        // assert
        expect(result).toEqual([-1, -1, -1, -1, -1]);
    });
});