力扣刷题记录2（无算法背景，纯C语言）

7、有效括号（20栈）

cpp 复制代码

bool isValid(char* s) 
{
    int len = strlen(s);
    if(len%2 != 0)return false;
    else if(len == 0)return false;
    int pStack = 0;
    char* Stack = (char *)malloc(sizeof(*s)*(len+1));
    for(int i=0; i<len; i++)
    {
        if(s[i] == '(')
        {

            Stack[pStack] = ')';
            pStack++;        
        }
        else if(s[i] == '[')
        {

            Stack[pStack] = ']';
            pStack++;        
        }
        else if(s[i] == '{')
        {

            Stack[pStack] = '}';
            pStack++;        
        }
        else
        {
            if(pStack == 0)return false;
            else if(Stack[pStack-1] == s[i])
            {
                pStack--;
            }
            else return false;
        }
    }
    if(pStack == 0)return true;
    else return false;
}

8、二叉树的中序遍历（94二叉树递归）

cpp 复制代码

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
/**
 * Note: The returned array must be malloced, assume caller calls free().
 */

void getnum(struct TreeNode* root,int *pNum,int *num)
{
    if (root == NULL) {
        return;
    }
    getnum(root -> left,pNum,num);
    num[(*pNum) ++] =root -> val;
    getnum(root -> right,pNum,num);
}

int* inorderTraversal(struct TreeNode* root, int* returnSize) {
    int pNum = 0;
    int *num = (int *)malloc(sizeof(int)*100);
    getnum(root,&pNum,num);
    *returnSize = pNum;
    return num;
}

9、二叉树最大深度（104二叉树遍历）

cpp 复制代码

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
int get_deep(struct TreeNode* root)
{
    int deep = 0;
    if(root == NULL)return 0;
    else deep++;
    int Left_deep = get_deep(root -> left);
    int Right_deep = get_deep(root -> right);
    return Left_deep>Right_deep?Left_deep+deep:Right_deep+deep;
}

int maxDepth(struct TreeNode* root) {
    return get_deep(root);
}

10、翻转二叉树（226二叉树递归）

cpp 复制代码

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */

void invert(struct TreeNode* root) 
{
    if(root == NULL)return;
    struct TreeNode* rootleft = root -> left;
    struct TreeNode* rootlright = root -> right;
    root -> left = rootlright;
    root -> right = rootleft;
    invert(root -> left);
    invert(root -> right);
}
struct TreeNode* invertTree(struct TreeNode* root) 
{
    invert(root);
    return root;
}

11.对称二叉树（101遍历二叉树）

cpp 复制代码

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */

bool isdydy(struct TreeNode* rootr,struct TreeNode* rootl)
{
    bool r = false;
    bool l = false;
    if(rootr == NULL && rootl == NULL)return true;
    if(rootr == NULL || rootl == NULL)return false;
    if(rootr->val == rootl->val)
    {
        r = isdydy(rootr->left,rootl->right);
        l = isdydy(rootr->right,rootl->left);
    }
    return r&&l;
}
bool isSymmetric(struct TreeNode* root) 
{
    if(root == NULL) return false;
    return isdydy(root -> left,root -> right);
}

12、无重复字符的最长子串（3双指针字符串滑动窗口）

cpp 复制代码

int lengthOfLongestSubstring(char* s) 
{
    int pPre = 0;//左
    int pBac = 0;//右
    int clong = 1;
    int len = strlen(s);
    if(len<=0)return 0;
    int Hashmap[128];
    memset(Hashmap,-1,sizeof(Hashmap)); 
    for(int i = 0; i < len; i ++)
    {
        if(Hashmap[(int)s[i]] < pPre)
        {
            Hashmap[(int)s[i]] = i;
            if (i > pBac)
            {
                pBac++;
                clong = pBac-pPre+1;
            }
        }
        else
        {
            pPre = Hashmap[(int)s[i]]+1;
            Hashmap[(int)s[i]] = i;
            pBac = pPre + clong - 1;
        }
        
    }
    return clong;
}