The next greater element of some element x in an array is the first greater element that is to the right of x in the same array.
You are given two distinct 0-indexed integer arrays nums1 and nums2, where nums1 is a subset of nums2.
For each 0 <= i < nums1.length, find the index j such that nums1[i] == nums2[j] and determine the next greater element of nums2[j] in nums2. If there is no next greater element, then the answer for this query is -1.
Return an array ans of length nums1.length such that ans[i] is the next greater element as described above.
Input: nums1 = [4,1,2], nums2 = [1,3,4,2]
Output: [-1,3,-1]
Explanation: The next greater element for each value of
nums1 is as follows:
- 4 is underlined in nums2 = [1,3,4,2].
There is no next greater element, so the
answer is -1.
- 1 is underlined in nums2 = [1,3,4,2]. The next
greater element is 3.
- 2 is underlined in nums2 = [1,3,4,2]. There is
no next greater element, so the answer is -1.Input: nums1 = [2,4], nums2 = [1,2,3,4]
Output: [3,-1]
Explanation: The next greater element for each value of
nums1 is as follows:
- 2 is underlined in nums2 = [1,2,3,4]. The next
greater element is 3.
- 4 is underlined in nums2 = [1,2,3,4]. There is
no next greater element, so the answer is -1.1 <= nums1.length <= nums2.length <= 10000 <= nums1[i], nums2[i] <= 10⁴- All integers in
nums1andnums2are unique. - All the integers of
nums1also appear innums2.
const nextGreaterElement = (nums1, nums2) => {
const map = {},
stack = [];
nums2.forEach(n => {
while (stack.length > 0 && stack[stack.length - 1] < n) {
map[stack.pop()] = n;
}
stack.push(n);
});
return nums1.map(n => map[n] || -1);
};I've coded a function called nextGreaterElement that takes in two arrays nums1 and nums2. The purpose of this function is to find the next greater element for each element in nums1 from the corresponding position in nums2 and return a new array with those values.
Inside the function, an empty object called map and an empty array called stack are initialized.
A forEach loop is used to iterate over each element n in the nums2 array. Within the loop, it checks if the stack array is not empty and if the last element in the stack array is smaller than n.
If the condition is true, it means that the next greater element for the last element in the stack array has been found. In this case, the function pops the last element from the stack array and assigns n as the value for the popped element in the map object.
After that, the function pushes n into the stack array.
The loop continues until all elements in the nums2 array have been processed. By the end of the loop, the map object contains the next greater element for each element in nums2.
Finally, a new array is returned by using the map method on the nums1 array. Within the map function, it checks if the current element n exists as a key in the map object. If it does, the corresponding value from the map object is returned. Otherwise, -1 is returned.
In summary, this function finds the next greater element for each element in nums1 from the corresponding position in nums2. It achieves this by using a stack to keep track of elements in nums2 and an object to store the next greater elements. The resulting values are returned as a new array.