下一个更大元素 I

/*
 * Problem: Find the next greater element for each element in nums1 from nums2 using Java Streams.
 * Approach: Utilize a HashMap to store the next greater element for elements in nums2, then use Streams to construct the result.
 */
 
import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
 
public class NextGreaterElementStream {
    public int[] nextGreaterElement(int[] nums1, int[] nums2) {
        // Stack and map as in the normal approach
        Stack<Integer> stack = new Stack<>();
        Map<Integer, Integer> map = new HashMap<>();
        
        // Populate the map with the next greater element
        for (int num : nums2) {
            while (!stack.isEmpty() && stack.peek() < num) {
                map.put(stack.pop(), num);
            }
            stack.push(num);
        }
        
        while (!stack.isEmpty()) {
            map.put(stack.pop(), -1);
        }
        
        // Use Streams to map each element in nums1 to its next greater element
        return IntStream.of(nums1)
                .map(map::get)
                .toArray();
    }
}