java链表递归的另一种实现方法

Question

这是一个linked list， 其中的一个method是给每个值+上一个x， 我理解递归思路，但是我想知道不用递归，iterative 的方式如何写。

public class IntList {
public int first;
public IntList rest;

public IntList(int f, IntList r) {
first = f;
rest = r;
}

/** Return the size of the list using... recursion! */
public int size() {
if (rest == null) {
return 1;
}
return 1 + this.rest.size();
}

/** Return the size of the list using no recursion! */
public int iterativeSize() {
IntList p = this;
int totalSize = 0;
while (p != null) {
totalSize += 1;
p = p.rest;
}
return totalSize;
}

/** Returns the ith value in this list.*/
public int get(int i) {

}

/** Returns an IntList identical to L, but with
* each element incremented by x. L is not allowed
* to change. */
/**我想知道这个incrList method不用递归，如何用iterative 的方式写出来 */
public static IntList incrList(IntList L, int x) {
if (L == null) {
return L;
}
IntList incr = new IntList(L.first + x, incrList(L.rest, x));
return incr; 
}

public static void main(String[] args) {
IntList L = new IntList(15, null);
L = new IntList(10, L);
L = new IntList(5, L);

System.out.println(L.iterativeSize());
}
} 

Answer 1

public class IntList {
    public int first;
    public IntList rest;

    public IntList(int f, IntList r) {
        first = f;
        rest = r;
    }

    /**
     * Return the size of the list using... recursion!
     */
    public int size() {
        if (rest == null) {
            return 1;
        }
        return 1 + this.rest.size();
    }

    /**
     * Return the size of the list using no recursion!
     */
    public int iterativeSize() {
        IntList p = this;
        int totalSize = 0;
        while (p != null) {
            totalSize += 1;
            p = p.rest;
        }
        return totalSize;
    }


/**
 * Returns an IntList identical to L, but with
 * each element incremented by x. L is not allowed
 * to change.
 *
 */
    /**
     * 我想知道这个incrList method不用递归，如何用iterative 的方式写出来
     */
    public static IntList incrList(IntList L, int x) {
        if (L == null) {
            return L;
        }
        IntList incr = new IntList(L.first + x, incrList(L.rest, x));
        return incr;
    }

    public static IntList incrList2(IntList L, int x) {
        if (L == null) {
            return L;
        }
        IntList temp = L;
        IntList incr = new IntList(temp.first + x, null);
        IntList temp2 = incr;
        while (temp.rest != null) {
            temp = temp.rest;
            temp2.rest = new IntList(temp.first + x, null);
            temp2 = temp2.rest;
        }
        return incr;
    }

    @Override
    public String toString() {
        return "IntList{" +
                "first=" + first +
                ", rest=" + rest +
                '}';
    }

    public static void main(String[] args) {
        IntList L = new IntList(15, null);
        L = new IntList(10, L);
        L = new IntList(5, L);
        System.out.println(L);
        System.out.println(IntList.incrList2(L, 1));
    }
}