496. Next Greater Element I

Posted 2021-02-28 shwzh1990

You are given two arrays (without duplicates) nums1 and nums2 where nums1’s elements are subset of nums2. Find all the next greater numbers for nums1‘s elements in the corresponding places of nums2.

The Next Greater Number of a number x in nums1 is the first greater number to its right in nums2. If it does not exist, output -1 for this number.

Example 1:
Input: nums1 = [4,1,2], nums2 = [1,3,4,2].
Output: [-1,3,-1]
Explanation:
For number 4 in the first array, you cannot find the next greater number for it in the second array, so output -1.
For number 1 in the first array, the next greater number for it in the second array is 3.
For number 2 in the first array, there is no next greater number for it in the second array, so output -1.
Example 2:
Input: nums1 = [2,4], nums2 = [1,2,3,4].
Output: [3,-1]
Explanation:
For number 2 in the first array, the next greater number for it in the second array is 3.
For number 4 in the first array, there is no next greater number for it in the second array, so output -1.
Note:
All elements in nums1 and nums2 are unique.
The length of both nums1 and nums2 would not exceed 1000.

先给出一个朴素的解法

int GetElement(int val, int index, int* nums2, int nums2Size)   //我们利用这个函数来找出是否在旁边有比这个元素大的元素
{
 int i = index;
 
 for(i ; i < nums2Size; i++)          
     if(val < nums2[i])
        return nums2[i];

  return -1;
}

/*
这个函数是找出 num1 的元素对应的num2 数组里面的位置
*/
int GetposInArray2(int val, int* nums2, int nums2Size)
{
    int  i ;
    for( i = 0; i < nums2Size; i++)
       if(val == nums2[i])
          return i;
    return -1;
}

int* nextGreaterElement(int* nums1, int nums1Size, int* nums2, int nums2Size, int* returnSize){
     
     int* result = (int*)malloc(sizeof(int)*nums1Size);                      //build a new array restore for return result
     *returnSize = nums1Size;                                                //这个数据的大小一定是跟array1 大小一样
     for(int i = 0; i < nums1Size; i++)                                      
       result[i] =  GetElement(nums1[i], GetposInArray2(nums1[i], nums2, nums2Size), nums2, nums2Size);
         
   
   return result;
}