两个大数相加

实现两个大数相加 包括字符串和 链表实现。

 public static void main(String[] args) {

       ListNode header = new ListNode(1);

        header.next = new ListNode(2);

        header.next.next = new ListNode(3);

        header.next.next.next = new ListNode(4);

        header.next.next.next.next = new ListNode(5);

       ListNode header1 = new ListNode(1);

       header1.next = new ListNode(2);

       header1.next.next = new ListNode(3);

       ListNode result = add(header,header1);

       while(result != null){

            System.out.print(result.value);

            result = result.next;

       }

  }

//链表反转

private static ListNode reverseList(ListNode head) { //1

    ListNode prev = null;  // 2

    ListNode curr = head;  // 3

    while (curr != null) {  //4

        ListNode nextTemp = curr.next; //5

        curr.next = prev;  // 6

        prev = curr;  //7

        curr = nextTemp; //8

    }

    return prev;  //9

}

//这是错误写法！！！

private static ListNode reverseListNode(ListNode header){

        if(header == null || header.next == null){

            return header;

        }

        printNodeList(header);

        ListNode preNode = header;

        ListNode curNode = header.next;

        while (curNode.next != null){

            ListNode temp = curNode.next;

            preNode.next = null;

            curNode.next = preNode;



            preNode = curNode;

            curNode = temp;

        }

        curNode.next = preNode;

        printNodeList(curNode);

        return curNode;

    }

    static void printNodeList(ListNode head){

     System.out.println("======start========");

        while(head != null){

            System.out.println(head.value);

            head = head.next;

        }

        System.out.println("======end========");

    }

  //链表

  private static ListNode add(ListNode header1,ListNode header2){

    if(header1 == null || header2 == null){

        return null;

    }

    header1 = reverseListNode(header1);

    header2 = reverseListNode(header2);

    ListNode result = null;

    ListNode curNode = null;

    int lastNum = 0;

      while(header1 != null || header2 != null){

        int num1 = header1 != null ? header1.value : 0;

        int num2 = header2 != null ? header2.value : 0;

          int sum = num1 + num2;

          int curNum =  sum > 10 ? (sum % 10) : sum;

          curNum += lastNum;

          lastNum = sum >= 10 ? 1 : 0;

        if(result == null){

            result = new ListNode();

            result.value = curNum;

            curNode = result;

        }else{

            curNode.next = new ListNode();

            curNode.next.value = curNum;

            curNode = curNode.next;

        }

        if(header1 != null){

            header1 = header1.next;

        }

        if(header2 != null){

            header2 = header2.next;

        }

      }

      if(lastNum > 0){

           curNode.next = new ListNode();

           curNode.next.value = lastNum;

      }

      return reverseListNode(result);

  }

  //字符串

  private static void addStr(String numStr1,String numStr2){

      if(numStr1 == null || numStr1 == null){

          return;

      }

      int l1 = numStr1.length();

      int l2 = numStr2.length();

      int maxLength = l1 > l2 ? l1 : l2;

      StringBuilder sbSum = new StringBuilder();

      int lastNum = 0;

      for(int i = 0;i < maxLength;i++){

          int num1 = l1 > i ? numStr1.charAt(l1 - 1 - i) - '0' : 0;

          int num2 = l2 > i ? numStr2.charAt(l2 - 1 - i) - '0' : 0;

          int sum = num1 + num2;

          int curNum =  sum > 10 ? (sum % 10) : sum;

          curNum += lastNum;

          lastNum = sum >= 10 ? 1 : 0;

          sbSum.append(String.valueOf(curNum));



      }

      if(lastNum > 0){

          sbSum.append(lastNum);

      }

      System.out.println(sbSum.reverse().toString());

  }

  static class ListNode{

      private ListNode next;

      private int value;

      public ListNode(){

          this(-1);

      }

      public ListNode(int value){

          this.value = value;

      }

  }