# Leetcode刷题笔记第1天

`java程序猿转go语言，通过leetcode刷题来熟悉go语言，完成语言基础和语法基础的熟悉`

## 1.两数之和

``````func twoSum(nums []int, target int) []int {
for i := 0; i < len(nums) - 1; i++ {
for j := i + 1; j < len(nums); j++ {
if (nums[j] + nums[i] == target) {
return []int {i, j};
}
}
}
return nil
}``````

``````func twoSum(nums []int, target int) []int {
hashmap := make(map[int] int)
for index, value := range nums {
if v, ok := hashmap[value]; ok {
return []int{index, v}
}
hashmap[target - value] = index
}
return nil
}``````

## 2.两数相加

`````` func addTwoNumbers(l1 *ListNode, l2 *ListNode) *ListNode {
return addTwoNumbersHelp(l1, l2, 0);
}
func addTwoNumbersHelp(l1 *ListNode, l2 *ListNode, add int) *ListNode {
if l1 == nil && l2 == nil && add == 0 {
return nil
}
if (l1 != nil) {
l1 = l1.Next
}
if (l2 != nil) {
l2 = l2.Next
}
node := ListNode{
}
return &node;
}``````

``````func addTwoNumbers(l1 *ListNode, l2 *ListNode) *ListNode {
for l1 != nil && l2 != nil {
add += l1.Val + l2.Val;
l1 = l1.Next;
l2 = l2.Next;
cur := ListNode{
Val: add % 10,
Next: nil,
}
tail.Next = &cur;
tail = &cur;
}
for l1 != nil {
l1 = l1.Next;
cur := ListNode{
Val: add % 10,
Next: nil,
}
tail.Next = &cur;
tail = &cur;
}
for l2 != nil {
l2 = l2.Next;
cur := ListNode{
Val: add % 10,
Next: nil,
}
tail.Next = &cur;
tail = &cur;
}
if add != 0 {
tail.Next = &ListNode{1,nil}
}
}``````

## 3.最长无重复子串

`直观的逻辑：哈希表记录字符存在的下标、如果存在过，则左边界等于原本左边界或者重复的字符的位置+1的位置中较大的，因为有可能重复字符不在如今最长子串的范围里，则左边界无需变化`

``````func lengthOfLongestSubstring1(s string) int {
res := 0;
m := make(map[byte] int);
left := 0;
for i := 0; i < len(s); i++ {
if _,ok := m[s[i]]; ok {
left = int(math.Max(float64(left), float64(m[s[i]]+1)));
}
m[s[i]] = i;
res = int(math.Max(float64(res), float64(i-left+1)))
}
return res;
}``````

`巧妙的只增大不减小窗口`

``````func lengthOfLongestSubstring(s string) int {
start,end := 0,0
for i := 0; i < len(s); i++ {
index := strings.Index(s[start:i],string(s[i]))
if index==-1{
if i+1>end{
end=i+1
}
}else{
start+=index+1
end+=index+1
}
}
return end-start
}``````