Recognize Recursive Function

Each of following functions solves some well-known problem, but name of the function is changed. Figure out what problems functions solve.

Exercise 1

int foo(int x) { 
    if (x == 0) return 0;
    if (x < 0) return foo(x+1) +1;
    if (x > 0) return foo(x-1) +1;
}

reveal

int absoluteValue(int x) { 
    if (x == 0) return 0;
    if (x < 0) return absoluteValue(x+1) +1;
    if (x > 0) return absoluteValue(x-1) +1;
}

WARNING

This function is just educative. Not for serious use at all, it is the worst implementation ever.

Exercise 2

long foo(int x) {
    if (x == 0) return 1;
    return x * foo(x-1);
}

reveal

long factorial(int x) {
    if (x == 0) return 1;
    return x * factorial(x-1);
}

TIP

This function is legit for serious use.

Exercise 3

int foo(int num) {
    if (num <= 0) return 0;
    if (num == 1) return 1;
    return foo(num-1) + foo(num-2);
}

reveal

int fibonacci(int num) {
    if (num <= 0) return 0;
    if (num == 1) return 1;
    return fibonacci(num-1) + fibonacci(num-2);
}

WARNING

This function is just educative. Not for serious use at all, it is the worst implementation ever.

Exercise 4

int foo(int num);

int bar(int num) {
    if (num < 0) return bar(-num);
    if (num == 0) return 0;
    if (num == 1) return 1;
    return foo(num-1);
}

int foo(int num) {
    if (num < 0) return foo(-num);
    if (num == 0) return 1;
    if (num == 1) return 0;
    return bar(num-1);
}

reveal

int isEven(int num);

int isOdd(int num) {
    if (num < 0) return isOdd(-num);
    if (num == 0) return 0;
    if (num == 1) return 1;
    return isEven(num-1);
}

int isEven(int num) {
    if (num < 0) return isEven(-num);
    if (num == 0) return 1;
    if (num == 1) return 0;
    return isOdd(num-1);
}

WARNING

These functions are just educative. Not for serious use at all, it is the worst implementation ever.