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_503.java
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_503.java
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package com.fishercoder.solutions;
import java.util.Stack;
public class _503 {
public static class Solution1 {
/**
* Credit: https://discuss.leetcode.com/topic/77881/typical-ways-to-solve-circular-array-problems-java-solution
* Note: we store INDEX into the stack, reversely, the larger index put at the bottom of the stack, the smaller index at the top
*/
public int[] nextGreaterElements(int[] nums) {
if (nums == null || nums.length == 0) {
return nums;
}
int len = nums.length;
Stack<Integer> stack = new Stack<>();
for (int i = len - 1; i >= 0; i--) {
stack.push(i);
//push all indexes into the stack reversely
}
int[] result = new int[len];
for (int i = len - 1; i >= 0; i--) {
result[i] = -1;
//initialize it to be -1 in case we cannot find its next greater element in the array
while (!stack.isEmpty() && (nums[stack.peek()] <= nums[i])) {
stack.pop();
}
if (!stack.isEmpty()) {
result[i] = nums[stack.peek()];
}
stack.push(i);
}
return result;
}
}
public static class Solution2 {
/**
* credit: https://leetcode.com/articles/next-greater-element-ii/
*/
public int[] nextGreaterElements(int[] nums) {
int[] result = new int[nums.length];
Stack<Integer> stack = new Stack<>();
for (int i = nums.length * 2 - 1; i >= 0; i--) {
while (!stack.isEmpty() && nums[stack.peek()] <= nums[i % nums.length]) {
stack.pop();
}
result[i % nums.length] = stack.isEmpty() ? -1 : nums[stack.peek()];
stack.push(i % nums.length);
}
return result;
}
}
}