Daily Temperatures

Author: vitalish

src/main/java/com/vitalish/leetcode/stack/DailyTemperatures.java

@@ -0,0 +1,46 @@
+package com.vitalish.leetcode.stack;
+
+import java.util.Stack;
+
+/**
+ * Daily Temperatures
+ *
+ * @see https://neetcode.io/problems/daily-temperatures
+ */
+public class DailyTemperatures {
+
+    // 0(n^2)
+    public int[] dailyTemperatures(int[] temperatures) {
+        int[] result = new int[temperatures.length];
+
+        for (int i = 0; i < temperatures.length; i++) {
+            int j = i;
+            int daysCount = 0;
+            while (j < temperatures.length && temperatures[i] >= temperatures[j]) {
+                daysCount++;
+                j++;
+            }
+            if (j == temperatures.length) {
+                result[i] = 0;
+            } else {
+                result[i] = daysCount;
+            }
+        }
+        return result;
+    }
+
+    // O(n)
+    public int[] dailyTemperatures2(int[] temperatures) {
+        int[] result = new int[temperatures.length];
+        Stack<Integer> stack = new Stack<>();
+
+        for (int i = 0; i < temperatures.length; i++) {
+            while (!stack.empty() && temperatures[i] > temperatures[stack.peek()]) {
+                int j = stack.pop();
+                result[j] = i - j;
+            }
+            stack.push(i);
+        }
+        return result;
+    }
+}

src/test/java/com/vitalish/leetcode/stack/DailyTemperaturesTest.java

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+package com.vitalish.leetcode.stack;
+
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+import java.util.stream.Stream;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+
+class DailyTemperaturesTest {
+
+    private final DailyTemperatures dailyTemperatures = new DailyTemperatures();
+
+    @ParameterizedTest
+    @MethodSource("arguments")
+    void calcDailyTemperatures(int[] temperatures, int[] expectedResult) {
+        assertArrayEquals(expectedResult, dailyTemperatures.dailyTemperatures(temperatures));
+    }
+
+    @ParameterizedTest
+    @MethodSource("arguments")
+    void calcDailyTemperatures2(int[] temperatures, int[] expectedResult) {
+        assertArrayEquals(expectedResult, dailyTemperatures.dailyTemperatures2(temperatures));
+    }
+
+
+    private static Stream<Arguments> arguments() {
+        return Stream.of(
+                Arguments.of(new int[]{30, 38, 30, 36, 35, 40, 28}, new int[]{1, 4, 1, 2, 1, 0, 0}),
+                Arguments.of(new int[]{22, 21, 20}, new int[]{0, 0, 0})
+        );
+    }
+}