recursion | Function 1, recursive function definition:
A: A recursive function, called a function, calls itself directly or indirectly in the body of a function, that is, the function's nesting is the function itself.
2, recursion way: recursive call has direct recursive and indirect recursion two kinds of way.
A: Direct recursion: The call function itself appears in the function.
Example 1: The following code asks the Fibonacci number, the first and second items of the Fibonacci series are 1, and then each of the preceding items is the sum of the first two items, i.e. 1, 1, 2, 3, 5, 8, 13 ....
Program code:
public class Test {
public static void Main (String args[]) {
int x1 = 1;
int sum = 0;
int n = 7;
for (int i = 1; I <= n; i++) {
X1 = func (i);
sum = sum + x1;
}
System.out.println ("sum=" + sum);
}
public static int func (int x) {
if (x > 2)
Return (func (x-1) + func (x-2));
Else
return 1;
}
}
B: Indirect recursion: The other function is called in the function, and the other function has called this function.
Example 2: Calculates the Fibonacci sequence by using the indirect recursive return.
Program code:
public class Test {
public static void Main (String args[]) {
int x1 = 1;
int sum = 0;
int n = 7;
for (int i = 1; I <= n; i++) {
X1 = func1 (i);
sum = sum + x1;
}
System.out.println ("sum=" + sum);
}
public static int func1 (int a) {
int b;
B=func2 (a);
return b;
}
public static int Func2 (int b) {
if (b> 2)
Return (Func1 (b-1) + func1 (b-2));
Else
return 1;
}
}
3. Why should I use a recursive function? What are the drawbacks of recursive functions?
A: The purpose of recursion is to simplify programming and make the program easy to read.
Example 3: The following recursive function is not used to compute the Fibonacci sequence.
Program code:
public class Test {
public static void Main (String args[]) {
int n=7;
int a=1, b=1, temp;
int sum=2;
for (int i=3; i<=n; i++) {
Temp=a+b; A=b; B=temp;
Sum=sum+temp;
}
System.out.println ("sum=" + sum);
}
}
From the above example we can find that although the non recursive function is efficient, but more difficult to program, the readability is poor. The disadvantage of a recursive function is that it increases the overhead of the system, which means that the stack memory takes up a bit more each time it is recursively.
4, the condition of the recursion:
A: You need to have the statement to complete the task to meet the recursive requirements (reduce rather than diverge).
5, the recursive Advanced step:
Example 4:
Solver: If a heifer starts a cow every year from the fourth year of birth, how many cows are there in the nth years?
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