LeetCode前3题

Two Sum

Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9, return [0, 1].

public static int[] twoSum(int[] numbers, int target) {        int[] result = new int[2];        Map<Integer, Integer> map = new HashMap<Integer, Integer>();        for (int i = 0; i < numbers.length; i++) {            if (map.containsKey(target - numbers[i])) {                result[1] = i;                result[0] = map.get(target - numbers[i]);                return result;            }            map.put(numbers[i], i);        }        return result;    }

Add Two Numbers

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.

You may assume the two numbers do not contain any leading zero, except
the number 0 itself.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4) Output: 7 -> 0 -> 8

class ListNode {     int val;     ListNode next;     ListNode(int x) { val = x; }}public ListNode addTwoNumbers(ListNode l1, ListNode l2) {       ListNode l3 = new ListNode(0);       ListNode m = l1;       ListNode n = l2;       ListNode result = l3;       int sum = 0;       int carry = 0;       while(m != null || n != null){           if (m != null){               sum += m.val;               m = m.next;           }           if(n != null){               sum += n.val;               n = n.next;           }           carry = sum / 10;           if(carry == 1)               result.next = new ListNode(sum % 10);           else               result.next = new ListNode(sum);           sum = carry;           result = result.next;       }       if(sum == 1)           result.next = new ListNode(sum);       return l3.next;}

Longest Substring Without Repeating Characters

Given a string, find the length of the longest substring without
repeating characters.

Examples:

Given “abcabcbb”, the answer is “abc”, which the length is 3.

Given “bbbbb”, the answer is “b”, with the length of 1.

Given “pwwkew”, the answer is “wke”, with the length of 3. Note that
the answer must be a substring, “pwke” is a subsequence and not a
substring.

public int lengthOfLongestSubstring(String s) {    int length = 0;    int curr = 0;    int start = 0;    int index= 0;    HashMap<Integer,Integer> map = new HashMap<>();    char[] s2ch = s.toCharArray();    int size = s2ch.length;    int value = 0;    for(int i = 0;i < size;i++){        value = s2ch[i];        if(!map.containsKey(value)){            curr++;            map.put(value,i);        }else{            if(curr > length){                length = curr;            }            start = map.get(value);            while(index<= start){                map.remove((int) s2ch[index]);                index++;            }            map.put(value,i);            curr = i - start;        }    }    return (curr > length) ? curr : length;}