剑指offer第二版题解系列（三）

最新推荐文章于 2022-06-18 13:53:47 发布

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剑指offer题解

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本文针对《剑指Offer第二版》中的20至29题进行了详细的代码实现与解析，涵盖了字符串验证、数组操作、链表处理、环形链表问题、链表反转、链表合并、二叉树子结构判断、二叉树对称性检查、矩阵打印等经典算法题目。

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写在开头：正值毕业生求职期间，翻一翻剑指offer的书籍，将其中的题目进行分析和代码编写，并将代码整理到csdn博客上，如果有错误，敬请指出！（此系列不提供题目原文，请参考书籍《剑指offer第二版》即可。）

Test20 - Test29系列

1. Test20.java

public class Test20{
    public static boolean isnum(String str)
    {
        if(str==null||str.length()<1)
            return false;
        int index =0;
        if(str.charAt(index)=='+'||str.charAt(index)=='-')
            index++;
        if(index>=str.length())
            return false;
        while(index<str.length()&&isshuzi(str,index))
            index++;
        if(index>=str.length())
            return true;
        if(str.charAt(index)=='.') {
            index++;
            if (index >= str.length())
                return false;
            while (index < str.length() && isshuzi(str, index))
                index++;
            if (index >= str.length())
                return true;
        }
        else{
            if(str.charAt(index)=='e'|| str.charAt(index)=='E')
                index++;
            if(index>=str.length())
                return false;
            else{
                if(str.charAt(index)=='+'||str.charAt(index)=='-')
                {   index++;
                    if(index>=str.length())
                        return false;
                     else {
                         while(index<str.length()&&isshuzi(str,index))
                         index++;
                         if(index>=str.length())
                            return true;
                    }

                }
            }
        }
        return false;
    }
    public static boolean isshuzi(String str,int index) {
        if (str.charAt(index) >= '0' && str.charAt(index) <= '9')
            return true;
        else
            return false;
    }
    public static void main(String[] args)
    {
        String  str = "+100e+5";
        System.out.println(isnum(str));
    }

}

2. Test21.java

public class Test21{
    public static int[] joSwap(int[] arr)
    {
        if(arr==null||arr.length<1)
            return null;
        int i = 0;
        int j = arr.length-1;
        while(i<=j)
        {
            if((arr[i]&0x1)==1)
                i++;
            else if((arr[i]&0x1)==0)
            {
                swap(arr,i,j);
                j--;
            }
        }
        return arr;
    }
    public static void swap(int[] arr,int i,int j){
        if(arr==null||arr.length<1)
            return;

        int temp;
        temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
    }
    public static void print(int[] arr)
    {
        if(arr==null||arr.length<1)
            return;
        for(int i : arr)
            System.out.print(i);
    }
    public static void main(String[] args)
    {
        int[] arr = {1,2,3,4,5};
        print(joSwap(arr));
    }

}

3. Test22.java

public class Test22{
    public static class LNode{
        int data;
        LNode next;
        public LNode(int data){
            this.data = data;
        }
    }
    public static LNode thKNode(LNode head,int k){
        if(head==null||k<=0)
            return null;
        LNode quick = head;
        LNode slow = head;
        int i = 1; //如果 k=1就直接返回头结点

            while (i < k && quick != null) {
                    ++i;
                    quick = quick.next;

            }
            if(i<=k&&quick==null)
                return null;//如果经过以上循环之后，i<k说明k已经超出链表的长度了，如果i=k且quick为空，说明给出的k比链表的长度大1；


            else {
                while (quick != null && quick.next != null) {
                    quick = quick.next;
                    slow = slow.next;
                }
            }

        return slow;
    }
    public static void main(String[] args)
    {
        LNode n1 = new LNode(1);
        LNode n2 = new LNode(2);
        LNode n3 = new LNode(3);
        LNode n4 = new LNode(4);
        n1.next = n2;
        n2.next = n3;
        n3.next = n4;
        n4.next = null;
        LNode head = n1;
        LNode node = thKNode(head,5);
        System.out.println(node.data);
    }
}

4. Test23.java

public class Test23{
    public static class LNode{
        int data;
        LNode next;
        public LNode(int data){
            this.data = data;
        }
    }
    public static LNode meetingNode(LNode head)
    {
        if(head==null)
            return null;
        LNode quick = head;
        LNode slow = head;
        if(quick==null||quick.next==null||quick.next.next==null)
            return null;
        while(quick!=null&&quick.next!=null&quick.next.next!=null){
            quick = quick.next.next;
            slow = slow.next;
            if(quick==slow)
                break;
        }
        return quick;
    }
    public static int crlnum(LNode head,LNode meetingNode)
    {
        if(head==null)
            return 0;
        LNode p = meetingNode.next;
        int num = 1;
        while(p!=meetingNode) {
            p = p.next;
            ++num;
        }
        return num;
    }
    public static LNode rkNode(LNode head,int num)
    {
        if(head==null)
            return null;
        LNode quick = head;
        LNode slow = head;
        int i = 1;
        while (i<=num)
        {
            quick = quick.next;
            ++i;
        }
        while(quick != slow)
        {
            quick = quick.next;
            slow = slow.next;
        }
        return slow;
    }
    public static void main(String[] args)
    {
        LNode n1 = new LNode(1);
        LNode n2 = new LNode(2);
        LNode n3 = new LNode(3);
        LNode n4 = new LNode(4);
        LNode n5 = new LNode(5);
        LNode n6 = new LNode(6);
        n1.next = n2;
        n2.next = n3;
        n3.next = n4;
        n4.next = n5;
        n5.next = n6;
        n6.next = n3;
        LNode head = n1;
        int num = crlnum(head,meetingNode(head));
        System.out.println(num);
        LNode Node = rkNode(head,num);
        System.out.println(Node.data);
    }
}

5. Test24.java

public class Test24{
    public static class LNode{
        int data;
        LNode next;
        public LNode(int data){
            this.data = data;
        }
    }
    public static LNode reverseLink(LNode head)
    {
        if(head==null)
            return null;
        LNode pre = null;
        LNode cur = head;
        LNode net = head.next;
        if(head.next==null)
            return head;
        while(net!=null)
        {
            cur.next = pre;
            pre = cur;
            cur = net;
            net = net.next;
        }
        return cur;
    }
    public static void main(String[] args)
    {
        LNode n1 = new LNode(1);
//        LNode n2 = new LNode(2);
//        LNode n3 = new LNode(3);
//        LNode n4 = new LNode(4);
        n1.next = null;
//        n1.next = n2;
//        n2.next = n3;
//        n3.next = n4;
//        n4.next = null;
        LNode head = n1;
        LNode node  = reverseLink(head);
        System.out.println(node.data);
    }
}

6. Test25.java

public class Test25{
    public static class LNode{
        int data;
        LNode next;
        public LNode(int data){
            this.data = data;
        }
    }
    public static LNode sumsort(LNode head1,LNode head2)
    {
        if(head1==null&&head2==null)
            return null;
        if(head1==null)
            return head2;
        if(head2==null)
            return head1;
        LNode cur1 = head1;
        //LNode net1 = head1.next;
        LNode cur2 = head2;
        //LNode net2 = head2.next;
        LNode head = null;
        if(cur1!=null&&cur2!=null&&cur1.data<=cur2.data) {
            head = cur1;
            cur1 = cur1.next;
            head.next = sumsort(cur1,cur2);
        }
        else if(cur1!=null&&cur2!=null&&cur2.data<cur1.data){
            head = cur2;
            cur2 = cur2.next;
            head.next = sumsort(cur1,cur2);
        }
       return head;
    }
    public static void printLink(LNode head)
    {
        if(head==null)
         return;
        LNode p = head;
        while(p!=null) {
            System.out.print(p.data);
            p = p.next;
        }

    }
    public static void main(String[] args)
    {
        LNode n1 = new LNode(1);
        LNode n2 = new LNode(3);
        LNode n3 = new LNode(4);
        LNode n4 = new LNode(2);
        LNode n5 = new LNode(5);
        LNode n6 = new LNode(6);
        n1.next = n2;
        n2.next = n3;
        n3.next = null;
        n4.next = n5;
        n5.next = n6;
        n6.next = null;
        LNode head1 = n1;
        LNode head2 = n4;
        printLink(sumsort(head1,head2));

    }
}

7. Test26.java

public class Test26{
    public static class BinaryTree{
        double data;
        BinaryTree left;
        BinaryTree right;
        public BinaryTree(double data)
        {
            this.data = data;
        }
    }
    public static boolean samesubTree(BinaryTree root1,BinaryTree root2)
    {
        if(root1==null||root2==null)
            return false;
        boolean result = false;
        if(equal(root1.data,root2.data)) {
            result = samesubTree2(root1.left, root2.left);
             if (!result)
                result = samesubTree(root1.left, root2);
            else  if (!result)
                result = samesubTree(root1.right, root2);
        }
        return result;
    }
    public static boolean samesubTree2(BinaryTree root1,BinaryTree root2)
    {
        if(root2==null)
            return true;
        if(root1==null)
            return false;
        boolean result = false;
        if(!equal(root1.data,root2.data))
            return false;
        else
            return samesubTree2(root1.left,root2.left)&&samesubTree2(root1.right, root2.right);
    }
    public static boolean equal(double d1,double d2)
    {
        if((d1-d2>-0.0000001)&&(d1-d2)<0.0000001)
            return true;
        else
            return false;
    }
    public static void main(String[] args)
    {
        BinaryTree t1 = new BinaryTree(8);
        BinaryTree t2 = new BinaryTree(8);
        BinaryTree t3= new BinaryTree(7);
        BinaryTree t4 = new BinaryTree(9);
        BinaryTree t5 = new BinaryTree(2);
        BinaryTree t6 = new BinaryTree(4);
        BinaryTree t7 = new BinaryTree(7);
        BinaryTree t8 = new BinaryTree(8);
        BinaryTree t9 = new BinaryTree(9);
        BinaryTree t10 = new BinaryTree(2);
        t1.left = t2;
        t1.right = t3;
        t2.left = t4;
        t2.right = t5;
        t5.left = t6;
        t6.right = t7;
        t4.left = null;
        t4.right = null;
        t6.right = null;
        t6.left = null;
        t7.left = null;
        t7.right = null;
        t8.left = t9;
        t8.right = t10;
        t9.left = null;
        t9.right = null;
        t10.left = null;
        t10.right = null;
        System.out.println(samesubTree(t1,t8));

    }
}

8. Test27.java

public class Test27{
    public static class BinaryTree{
        int data;
        BinaryTree left;
        BinaryTree right;
        public BinaryTree(int data)
        {
            this.data = data;

        }
    }
    public static void reverse(BinaryTree root)
    {
        if(root==null)
            return ;
        if(root.left==null&&root.right==null)
            return ;
        if(root.left!=null&&root.right!=null) {
            BinaryTree node = root.left;
            root.left = root.right;
            root.right = node;
            reverse(root.left);
            reverse(root.right);
        }
        else if(root.left==null) {
            root.left = root.right;
            root.right = null;
            reverse(root.left);
        }
        else if(root.right == null)
        {
            root.right = root.left;
            root.left = null;
            reverse(root.right);
        }
    }
    public static void print(BinaryTree root)
    {
        if(root==null)
            return;
        System.out.println(root.data);
        print(root.left);
        print(root.right);
    }
   public static void main(String[] args)
   {
       BinaryTree t1 = new BinaryTree(8);
       BinaryTree t2 = new BinaryTree(8);
       BinaryTree t3 = new BinaryTree(7);
       BinaryTree t4 = new BinaryTree(9);
       BinaryTree t5 = new BinaryTree(2);
       BinaryTree t6 = new BinaryTree(4);
       BinaryTree t7 = new BinaryTree(7);
       t1.left = t2;
       t1.right = t3;
       t2.left = t4;
       t2.right = t5;
       t5.left = t6;
       t5.right = t7;
       t4.left = null;
       t4.right = null;
       t6.right = null;
       t6.left = null;
       t7.left = null;
       t7.right = null;
//         t1.left = null;
//         t1.right = null;
       reverse(t1);
       print(t1);

   }
}

9. Test28.java

public class Test28{
    public static class BinaryTree{
        int data;
        BinaryTree left;
        BinaryTree right;
        public BinaryTree(int data)
        {
            this.data = data;

        }
    }
    public static boolean isSymmerial(BinaryTree root)
    {
        if(root==null)
            return true;
        else
            return isSymmerial(root,root);
    }
    public static boolean isSymmerial(BinaryTree root1,BinaryTree root2)
    {
        if(root1==null&&root2==null)
            return true;
        if(root1==null||root2==null)
            return false;
        if(root1.data!=root2.data)
            return false;
        else
            return isSymmerial(root1.left,root2.right)&&isSymmerial(root1.right,root2.left);
    }
    public static void main(String[] args)
    {
        BinaryTree t1 = new BinaryTree(8);
        BinaryTree t2 = new BinaryTree(8);
        BinaryTree t3 = new BinaryTree(7);
        BinaryTree t4 = new BinaryTree(9);
        BinaryTree t5 = new BinaryTree(2);
        BinaryTree t6 = new BinaryTree(4);
        BinaryTree t7 = new BinaryTree(7);
        t1.left = t2;
        t1.right = t3;
        t2.left = t4;
        t2.right = t5;
        t5.left = t6;
        t5.right = t7;
        t4.left = null;
        t4.right = null;
        t6.right = null;
        t6.left = null;
        t7.left = null;
        t7.right = null;
        System.out.println(isSymmerial(t1));
    }
}

10. Test29.java

public class Test29{
    public static void printMatrix(int[][] numbers,int rows,int cols)
    {
        if(numbers==null||rows<1||cols<1)
            return;
        int start = 0;
        while(rows>start*2&&cols>start*2) {
            printMatrix1(numbers, rows, cols, start);
            start++;
        }
        return;
    }
    public static void printMatrix1(int[][] numbers,int rows,int cols,int start){
        int endX = cols-1-start;
        int endY = rows-1-start;
        for(int i = start;i<=endX;i++)
        {
            print(numbers[start][i]);
        }
        if(start<endY) {
            for (int i = start + 1; i <= endY; i++) {
                print(numbers[i][endX]);
            }
        }
        if(start<endX)
        {
            for(int i=endX-1;i>=start;i--)
            {
                print(numbers[endY][i]);
            }
        }
        if(start<endY-1&&start<endX)
        {
            for(int i=endY-1;i>start;i--)
                print(numbers[i][start]);
        }
        return;
    }
    public static void print(int num)
    {
        System.out.print(num);
    }

    public static void main(String[] args)
    {
        int[][] numbers = {{1,2,3,4},{5,6,7,8},{9,10,11,12},{13,14,15,16}};
        printMatrix(numbers,4,4);

    }
}