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src/class25/Code01_MonotonousStackForNowcoder.java

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+package class25;
+
+// 测试链接 : https://www.nowcoder.com/practice/2a2c00e7a88a498693568cef63a4b7bb
+// 如果在牛客上做题，可以用如下的方式来做
+// 提交如下的代码，并把主类名改成"Main"
+// 可以直接通过
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+
+public class Code01_MonotonousStackForNowcoder {
+
+	public static int[] arr = new int[1000000];
+	public static int[][] ans = new int[1000000][2];
+	public static int[] stack1 = new int[1000000];
+	public static int[] stack2 = new int[1000000];
+
+	public static void main(String[] args) throws IOException {
+		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+		int n = Integer.parseInt(br.readLine());
+		String[] strs = br.readLine().split(" ");
+		for (int i = 0; i < n; i++) {
+			arr[i] = Integer.parseInt(strs[i]);
+		}
+		getNearLess(n);
+		StringBuilder builder = new StringBuilder();
+		for (int i = 0; i < n; i++) {
+			builder.append(ans[i][0] + " " + ans[i][1] + "\n");
+		}
+		System.out.println(builder.toString());
+	}
+
+	public static void getNearLess(int n) {
+		int stackSize1 = 0;
+		int stackSize2 = 0;
+		for (int i = 0; i < n; i++) {
+			while (stackSize1 > 0 && arr[stack1[stackSize1 - 1]] > arr[i]) {
+				int curIndex = stack1[--stackSize1];
+				int left = stackSize2 < 2 ? -1 : stack2[stackSize2 - 2];
+				ans[curIndex][0] = left;
+				ans[curIndex][1] = i;
+				if (stackSize1 == 0 || arr[stack1[stackSize1 - 1]] != arr[curIndex]) {
+					stackSize2--;
+				}
+			}
+			if (stackSize1 != 0 && arr[stack1[stackSize1 - 1]] == arr[i]) {
+				stack2[stackSize2 - 1] = i;
+			} else {
+				stack2[stackSize2++] = i;
+			}
+			stack1[stackSize1++] = i;
+		}
+		while (stackSize1 != 0) {
+			int curIndex = stack1[--stackSize1];
+			int left = stackSize2 < 2 ? -1 : stack2[stackSize2 - 2];
+			ans[curIndex][0] = left;
+			ans[curIndex][1] = -1;
+			if (stackSize1 == 0 || arr[stack1[stackSize1 - 1]] != arr[curIndex]) {
+				stackSize2--;
+			}
+		}
+	}
+
+}