力扣数据结构刷题知识点分享 sort 和哈希表

• 数据结构
• • qsort（） & sort（）
  • • qsort()， c
    • sort（），c++
  • 哈希表
  • • C 语言
    • C++

qsort()函数是C 标准库 - ,
sort（）函数是c++中
void qsort(void *base, size_t nitems, size_t size, int (*compar)(const void , const void))

#include 
#include 

int cmp(const void* a, const void* b) {

    return  ( *(int*)a - *(int*)b );   //强制转换为int型指针然后解引用。
    //升序
}
int main(){
    qsort(nums, numsSize,sizeof(int),cmp) ;
   }

#include
 
bool cmp(int a,int b){
    return a>b;
   //降序排列
}
int main(){
    int a[10]={5,5,6,8,2,1,3};
    sort(a,a+10,cmp);//降序排列
}

两数之和
https://blog.csdn.net/nameofcsdn/article/details/107297361
哈希表知识

链接: https://blog.csdn.net/nameofcsdn/article/details/107297361

#include "uthash.h"

struct hashTable {
    int key;
    int val;
    UT_hash_handle hh;
};

struct hashTable* hashtable;

struct hashTable* find(int ikey) {
    struct hashTable* tmp;
    HASH_FIND_INT(hashtable, &ikey, tmp);  //在"uthash.h"里定义的
    return tmp;
}

void insert(int ikey, int ival) {
    struct hashTable* it = find(ikey);
    if (it == NULL) {
        struct hashTable* tmp = malloc(sizeof(struct hashTable));
        tmp->key = ikey, tmp->val = ival;
        HASH_ADD_INT(hashtable, key, tmp);
    } else {
        it->val = ival;
    }
}

int* twoSum(int* nums, int numsSize, int target, int* returnSize) {
    hashtable = NULL;
    for (int i = 0; i < numsSize; i++) {
        struct hashTable* it = find(target - nums[i]);
        if (it != NULL) {
            int* ret = malloc(sizeof(int) * 2);
            ret[0] = it->val, ret[1] = i;
            *returnSize = 2;
            return ret;
        }
        insert(nums[i], i);
    }
    *returnSize = 0;
    return NULL;
}

class Solution {
public:
    vector twoSum(vector& nums, int target) {
        unordered_map hashtable;
        for (int i = 0; i < nums.size(); ++i) {
            auto it = hashtable.find(target - nums[i]);
            if (it != hashtable.end()) {
                return {it->second, i};
            }
            hashtable[nums[i]] = i;
        }
        return {};
    }
};

作者：LeetCode-Solution
链接：https://leetcode.cn/problems/two-sum/solution/liang-shu-zhi-he-by-leetcode-solution/
来源：力扣（LeetCode）