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.
Example 1:
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.
Example 2:
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.
Constraints:
- 1 <= nums1.length <= nums2.length <= 1000
- 0 <= nums1[i], nums2[i] <= 104
- All integers in nums1 and nums2 are unique.
- All the integers of nums1 also appear in nums2.
Solution
class Solution {
public int[] nextGreaterElement(int[] findNums, int[] nums) {
Map<Integer, Integer> map = new HashMap<>();
int[] res = new int[findNums.length];
Deque<Integer> stack = new ArrayDeque<>();
for (int i = 0; i < nums.length; i++) {
while (!stack.isEmpty() && stack.peek() < nums[i]) {
map.put(stack.pop(), nums[i]);
}
stack.push(nums[i]);
}
while (!stack.isEmpty()) {
map.put(stack.pop(), -1);
}
for (int i = 0; i < findNums.length; i++) {
res[i] = map.get(findNums[i]);
}
return res;
}
public int[] nextGreaterElement2(int[] nums1, int[] nums2) {
Map<Integer, Integer> valueToIndex = new HashMap<>();
for (int i = 0; i < nums2.length; i++) {
valueToIndex.put(nums2[i], i);
}
int[] res = new int[nums1.length];
Arrays.fill(res, -1);
for (int i = 0; i < nums1.length; i++) {
Integer index = valueToIndex.get(nums1[i]);
if (index != null) {
for (int j = index + 1; j < nums2.length; j++) {
if (nums2[j] > nums1[i]) {
res[i] = nums2[j];
break;
}
}
}
}
return res;
}
}
Solution 2021-10-22
class Solution {
public int[] nextGreaterElement(int[] nums1, int[] nums2) {
Map<Integer, Integer> map = new HashMap<>();
Stack<Integer> stack = new Stack<>();
// [1,3,4,2]
// 1 = 3, 3 = 4, 2 = -1
for (int i = 0; i < nums2.length; i++) {
while (stack.size() > 0 && stack.peek() < nums2[i]) {
map.put(stack.pop(), nums2[i]);
}
stack.push(nums2[i]);
}
while (stack.size() > 0) {
map.put(stack.pop(), -1);
}
int[] res = new int[nums1.length];
for (int i = 0; i < nums1.length; i++) {
res[i] = map.get(nums1[i]);
}
return res;
}
}
Solution 2021-11-20
class Solution {
public int[] nextGreaterElement(int[] nums1, int[] nums2) {
Stack<Integer> stack = new Stack<>();
Map<Integer, Integer> nextGreater = new HashMap<>();
for (int i = 0; i < nums2.length; i++) {
while (stack.size() > 0 && nums2[stack.peek()] < nums2[i]) {
nextGreater.put(nums2[stack.pop()], nums2[i]);
}
stack.push(i);
}
int[] res = new int[nums1.length];
for (int i = 0; i < res.length; i++) {
res[i] = nextGreater.getOrDefault(nums1[i], -1);
}
return res;
}
}