Stack recursion Practice questions
Duration: 3 min
This video lesson is available to enrolled students.
AI Summary
An AI-generated summary of this video lecture.
The video presents a computer science problem involving a recursive function named `fun(int x, int y)`. The instructor systematically breaks down the execution of the function by tracing each recursive step on a digital whiteboard. The function logic is defined with a base case `if (x == 0) return y;` and a recursive step `return fun(x - 1, x + y);`. The instructor starts by initializing the parameters `x=4` and `y=3`. He then demonstrates how the function calls itself with modified arguments, decrementing `x` by 1 and adding the current value of `x` to `y` in each step. This process continues until the base case is met. The final result is identified as 13, corresponding to option (A).
Chapters
0:00 – 2:00 00:00-02:00
In this initial segment, the instructor introduces the problem statement and the function definition. He writes `fun(4, 3)` on the board and assigns the initial values `x=4` and `y=3`. He checks the condition `if (x == 0)`, which evaluates to false. Consequently, he proceeds to the recursive call `fun(x - 1, x + y)`. He writes down the next call `fun(3, 7)`, showing the calculation `4-1=3` and `4+3=7`. He continues this process, writing `fun(2, 10)` where `x` becomes 2 and `y` becomes `3+7=10`. The instructor then writes `fun(1, 12)`, updating `x` to 1 and `y` to `2+10=12`. The board fills with the sequence of function calls, illustrating the recursive nature of the code.
2:00 – 3:15 02:00-03:15
In the final segment, the instructor completes the trace of the recursive function. He writes the next call `fun(0, 13)`, where `x` becomes 0 and `y` becomes `1+12=13`. At this point, the condition `if (x == 0)` evaluates to true. The instructor indicates that the function returns the value of `y`, which is 13. He circles the number 13 on the board to highlight the final result. He then writes `(13) Ans` and places a checkmark next to option (A) 13, confirming it as the correct answer.
The lesson effectively demonstrates the evaluation of a recursive function by manually tracing its execution stack. By breaking down the problem into discrete steps, the instructor clarifies how parameters change with each recursive call. The visual aid of writing out each call on the board helps students follow the logic, from the initial call `fun(4, 3)` down to the base case `fun(0, 13)`. This methodical approach ensures a clear understanding of how the final value is derived through successive additions and decrements.