leetcode-month1-week1

Add Two Numbers

package ygy.test.week1;/** * Created by guoyao on 2017/9/3. */public class AddTwoNumbers {    /**     * You are given two non-empty linked lists representing two non-negative integers.     * The digits are stored in reverse order and each of their nodes contain a single digit.     * Add the two numbers and return it as a linked list.     * Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)     * Output: 7 -> 0 -> 8     */    public static void main(String[] args) throws Exception {        ListNode l1 = new ListNode(9);        //ListNode node2 = new ListNode(8);        //ListNode node3 = new ListNode(9);        ListNode headNode=new ListNode(0);        ListNode temp  = headNode ;        ListNode l2 = new ListNode(1);        for(int i = 0 ; i < 9 ;i ++ ) {            temp.next=new ListNode(9);            temp = temp.next ;        }        l2.next = headNode.next ;        ListNode listNode=addTwoNumbers(l1, l2);       do {           System.out.println(listNode.val);           listNode=listNode.next;       }while (listNode != null );    }    //正解    public ListNode addTwoNumbers_lettCode_answer(ListNode l1, ListNode l2) {        ListNode dummyHead = new ListNode(0);        ListNode p = l1, q = l2, curr = dummyHead;        int carry = 0;        while (p != null || q != null) {            int x = (p != null) ? p.val : 0;            int y = (q != null) ? q.val : 0;            int sum = carry + x + y;            carry = sum / 10;            curr.next = new ListNode(sum % 10);            curr = curr.next;            if (p != null) p = p.next;            if (q != null) q = q.next;        }        if (carry > 0) {            curr.next = new ListNode(carry);        }        return dummyHead.next;    }    //会超出int 和long的界限    public static ListNode addTwoNumbers(ListNode l1, ListNode l2) throws Exception {        StringBuilder l1Builder=new StringBuilder();        while (l1 != null) {            l1Builder.append(l1.val);            l1 = l1.next;        }        l1Builder.reverse();        long l1Num=Long.valueOf(l1Builder.toString());        l1Builder=new StringBuilder();        while (l2 != null) {            l1Builder.append(l2.val);            l2 = l2.next;        }        l1Builder.reverse();        long l2Num=Long.valueOf(l1Builder.toString());        long l3Num=l1Num + l2Num;        //将l3转化为 listNode        char[] chars=String.valueOf(l3Num).toCharArray();        ListNode tempNode=new ListNode( 0);        ListNode l3 = tempNode ;        for(int i = chars.length - 1 ;i >= 0 ; i --) {            l3.next=new ListNode(Integer.valueOf(""+chars[i]));            l3 = l3.next;        }        return  tempNode.next ;    }} class ListNode {    int val;    ListNode next;    ListNode(int x) { val = x; }}

Two Sum

package ygy.test.week1;import java.util.Arrays;/** * Created by guoyao on 2017/9/3. */public class TwoSum {    /**     * Given nums = [2, 7, 11, 15], target = 9,     * Because nums[0] + nums[1] = 2 + 7 = 9,     * return [0, 1].     */    public static void main(String[] args) {        int[] nums = {2, 7, 11, 15} ;        System.out.println(Arrays.toString(twoSum(nums,26)));    }    public static int[] twoSum(int[] nums, int target) {        for( int i = 0 ; i < nums.length -1 ; i ++) {   // n- 1            for(int j = i + 1; j < nums.length; j ++) {   // n                int result= nums[i] + nums[j];                if (result == target) {           //时间复杂度O(n2)                    return new int[]{i,j};                }            }        }        return  null ;    }}