//单调栈结构

import java.util.*;
//单调栈结构
public class Main_142 {
    public static int[][] getNearLessRepeat(int[] arr) {
        ArrayDeque<List<Integer>> stack = new ArrayDeque<>();
        int[][] res = new int[arr.length][2];
        for (int i = 0; i < arr.length; i++) {
            while (!stack.isEmpty() && arr[i] < arr[stack.peek().get(0)]) {
                List<Integer> topList = stack.pop();
                int leftLessIdx = stack.isEmpty() ? -1 : stack.peek().get(stack.peek().size() - 1);
                for (Integer n : topList) {
                    res[n][0] = leftLessIdx;
                    res[n][1] = i;
                }
            }
            if (!stack.isEmpty() && arr[i] == arr[stack.peek().get(0)]) {
                stack.peek().add(i);
            } else {
                List<Integer> list = new ArrayList<>();
                list.add(i);
                stack.push(list);
            }
        }
        while (!stack.isEmpty()) {
            List<Integer> topList = stack.pop();
            int leftLessIdx = stack.isEmpty() ? -1 : stack.peek().get(stack.peek().size() - 1);
            for (Integer n : topList) {
                res[n][0] = leftLessIdx;
                res[n][1] = -1;
            }
        }
        return res;
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) {
            arr[i] = sc.nextInt();
        }
        int[][] res = getNearLessRepeat(arr);
        for (int i = 0; i < n; i++) {
            System.out.println(res[i][0] + " " + res[i][1]);
        }
    }
}


//import java.util.Scanner;
//import java.util.Stack;
//
//public class Main_142 {
//    public static void main(String[] args) {
//        Scanner scanner = new Scanner(System.in);
//
//        while (scanner.hasNext()) {
//            int num = scanner.nextInt();
//            int[] arr = new int[num];
//            for (int i = 0; i < num; i++) {
//                arr[i] = scanner.nextInt();
//            }
//
//            Stack<Integer> stack = new Stack<>();
//
//        }
//    }
//}

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转载自blog.csdn.net/TIANHE_/article/details/107424782