Added tasks 3151-3154

src/main/java/g3101_3200/s3151_special_array_i/Solution.java

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+package g3101_3200.s3151_special_array_i;
+
+// #Easy #Array #2024_05_22_Time_0_ms_(100.00%)_Space_43.2_MB_(51.16%)
+
+public class Solution {
+    public boolean isArraySpecial(int[] nums) {
+        for (int i = 1; i < nums.length; i++) {
+            if (nums[i - 1] % 2 == 1 && nums[i] % 2 == 1) {
+                return false;
+            }
+            if (nums[i - 1] % 2 == 0 && nums[i] % 2 == 0) {
+                return false;
+            }
+        }
+        return true;
+    }
+}

src/main/java/g3101_3200/s3151_special_array_i/readme.md

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+3151\. Special Array I
+
+Easy
+
+An array is considered **special** if every pair of its adjacent elements contains two numbers with different parity.
+
+You are given an array of integers `nums`. Return `true` if `nums` is a **special** array, otherwise, return `false`.
+
+**Example 1:**
+
+**Input:** nums = [1]
+
+**Output:** true
+
+**Explanation:**
+
+There is only one element. So the answer is `true`.
+
+**Example 2:**
+
+**Input:** nums = [2,1,4]
+
+**Output:** true
+
+**Explanation:**
+
+There is only two pairs: `(2,1)` and `(1,4)`, and both of them contain numbers with different parity. So the answer is `true`.
+
+**Example 3:**
+
+**Input:** nums = [4,3,1,6]
+
+**Output:** false
+
+**Explanation:**
+
+`nums[1]` and `nums[2]` are both odd. So the answer is `false`.
+
+**Constraints:**
+
+*   `1 <= nums.length <= 100`
+*   `1 <= nums[i] <= 100`

src/main/java/g3101_3200/s3152_special_array_ii/Solution.java

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+package g3101_3200.s3152_special_array_ii;
+
+// #Medium #Array #Binary_Search #Prefix_Sum #2024_05_22_Time_2_ms_(99.93%)_Space_97.9_MB_(79.71%)
+
+public class Solution {
+    public boolean[] isArraySpecial(int[] nums, int[][] queries) {
+        int n = nums.length;
+        int[] bad = new int[n];
+        for (int i = 1; i < n; i++) {
+            bad[i] = bad[i - 1] + (((nums[i - 1] ^ nums[i]) & 1) ^ 1);
+        }
+        int nq = queries.length;
+        boolean[] res = new boolean[nq];
+        for (int i = 0; i < nq; i++) {
+            int[] q = queries[i];
+            res[i] = calc(bad, q[0], q[1]) == 0;
+        }
+        return res;
+    }
+
+    private int calc(int[] arr, int st, int end) {
+        return arr[end] - arr[st];
+    }
+}

src/main/java/g3101_3200/s3152_special_array_ii/readme.md

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+3152\. Special Array II
+
+Medium
+
+An array is considered **special** if every pair of its adjacent elements contains two numbers with different parity.
+
+You are given an array of integer `nums` and a 2D integer matrix `queries`, where for <code>queries[i] = [from<sub>i</sub>, to<sub>i</sub>]</code> your task is to check that subarray <code>nums[from<sub>i</sub>..to<sub>i</sub>]</code> is **special** or not.
+
+Return an array of booleans `answer` such that `answer[i]` is `true` if <code>nums[from<sub>i</sub>..to<sub>i</sub>]</code> is special.
+
+**Example 1:**
+
+**Input:** nums = [3,4,1,2,6], queries = [[0,4]]
+
+**Output:** [false]
+
+**Explanation:**
+
+The subarray is `[3,4,1,2,6]`. 2 and 6 are both even.
+
+**Example 2:**
+
+**Input:** nums = [4,3,1,6], queries = [[0,2],[2,3]]
+
+**Output:** [false,true]
+
+**Explanation:**
+
+1.  The subarray is `[4,3,1]`. 3 and 1 are both odd. So the answer to this query is `false`.
+2.  The subarray is `[1,6]`. There is only one pair: `(1,6)` and it contains numbers with different parity. So the answer to this query is `true`.
+
+**Constraints:**
+
+*   <code>1 <= nums.length <= 10<sup>5</sup></code>
+*   <code>1 <= nums[i] <= 10<sup>5</sup></code>
+*   <code>1 <= queries.length <= 10<sup>5</sup></code>
+*   `queries[i].length == 2`
+*   `0 <= queries[i][0] <= queries[i][1] <= nums.length - 1`

src/main/java/g3101_3200/s3153_sum_of_digit_differences_of_all_pairs/Solution.java

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+package g3101_3200.s3153_sum_of_digit_differences_of_all_pairs;
+
+// #Medium #Array #Hash_Table #Math #Counting #2024_05_22_Time_12_ms_(100.00%)_Space_62.8_MB_(6.25%)
+
+public class Solution {
+    public long sumDigitDifferences(int[] nums) {
+        long result = 0;
+        while (nums[0] > 0) {
+            int[] counts = new int[10];
+            for (int i = 0; i < nums.length; i++) {
+                int digit = nums[i] % 10;
+                nums[i] = nums[i] / 10;
+                result += i - counts[digit];
+                counts[digit]++;
+            }
+        }
+        return result;
+    }
+}

src/main/java/g3101_3200/s3153_sum_of_digit_differences_of_all_pairs/readme.md

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+3153\. Sum of Digit Differences of All Pairs
+
+Medium
+
+You are given an array `nums` consisting of **positive** integers where all integers have the **same** number of digits.
+
+The **digit difference** between two integers is the _count_ of different digits that are in the **same** position in the two integers.
+
+Return the **sum** of the **digit differences** between **all** pairs of integers in `nums`.
+
+**Example 1:**
+
+**Input:** nums = [13,23,12]
+
+**Output:** 4
+
+**Explanation:** 
+ We have the following: 
+ - The digit difference between **1**3 and **2**3 is 1. 
+ - The digit difference between 1**3** and 1**2** is 1. 
+ - The digit difference between **23** and **12** is 2. 
+ So the total sum of digit differences between all pairs of integers is `1 + 1 + 2 = 4`.
+
+**Example 2:**
+
+**Input:** nums = [10,10,10,10]
+
+**Output:** 0
+
+**Explanation:** 
+ All the integers in the array are the same. So the total sum of digit differences between all pairs of integers will be 0.
+
+**Constraints:**
+
+*   <code>2 <= nums.length <= 10<sup>5</sup></code>
+*   <code>1 <= nums[i] < 10<sup>9</sup></code>
+*   All integers in `nums` have the same number of digits.

src/main/java/g3101_3200/s3154_find_number_of_ways_to_reach_the_k_th_stair/Solution.java

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+package g3101_3200.s3154_find_number_of_ways_to_reach_the_k_th_stair;
+
+// #Hard #Dynamic_Programming #Math #Bit_Manipulation #Memoization #Combinatorics
+// #2024_05_22_Time_0_ms_(100.00%)_Space_40.3_MB_(98.50%)
+
+public class Solution {
+    public int waysToReachStair(int k) {
+        int x = 1;
+        int y = 1;
+        int a = 0;
+        while (x > 0 && x - y <= k) {
+            if (x >= k) {
+                a += combi(y, x - k);
+            }
+            x <<= 1;
+            y++;
+        }
+        return a;
+    }
+
+    private int combi(int a, int b) {
+        if (b > a - b) {
+            b = a - b;
+        }
+        long r = 1;
+        for (int i = 0; i < b; i++) {
+            r *= (a - i);
+            r /= (i + 1);
+        }
+        return (int) r;
+    }
+}

src/main/java/g3101_3200/s3154_find_number_of_ways_to_reach_the_k_th_stair/readme.md

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+3154\. Find Number of Ways to Reach the K-th Stair
+
+Hard
+
+You are given a **non-negative** integer `k`. There exists a staircase with an infinite number of stairs, with the **lowest** stair numbered 0.
+
+Alice has an integer `jump`, with an initial value of 0. She starts on stair 1 and wants to reach stair `k` using **any** number of **operations**. If she is on stair `i`, in one **operation** she can:
+
+*   Go down to stair `i - 1`. This operation **cannot** be used consecutively or on stair 0.
+*   Go up to stair <code>i + 2<sup>jump</sup></code>. And then, `jump` becomes `jump + 1`.
+
+Return the _total_ number of ways Alice can reach stair `k`.
+
+**Note** that it is possible that Alice reaches the stair `k`, and performs some operations to reach the stair `k` again.
+
+**Example 1:**
+
+**Input:** k = 0
+
+**Output:** 2
+
+**Explanation:**
+
+The 2 possible ways of reaching stair 0 are:
+
+*   Alice starts at stair 1.
+    *   Using an operation of the first type, she goes down 1 stair to reach stair 0.
+*   Alice starts at stair 1.
+    *   Using an operation of the first type, she goes down 1 stair to reach stair 0.
+    *   Using an operation of the second type, she goes up 2<sup>0</sup> stairs to reach stair 1.
+    *   Using an operation of the first type, she goes down 1 stair to reach stair 0.
+
+**Example 2:**
+
+**Input:** k = 1
+
+**Output:** 4
+
+**Explanation:**
+
+The 4 possible ways of reaching stair 1 are:
+
+*   Alice starts at stair 1. Alice is at stair 1.
+*   Alice starts at stair 1.
+    *   Using an operation of the first type, she goes down 1 stair to reach stair 0.
+    *   Using an operation of the second type, she goes up 2<sup>0</sup> stairs to reach stair 1.
+*   Alice starts at stair 1.
+    *   Using an operation of the second type, she goes up 2<sup>0</sup> stairs to reach stair 2.
+    *   Using an operation of the first type, she goes down 1 stair to reach stair 1.
+*   Alice starts at stair 1.
+    *   Using an operation of the first type, she goes down 1 stair to reach stair 0.
+    *   Using an operation of the second type, she goes up 2<sup>0</sup> stairs to reach stair 1.
+    *   Using an operation of the first type, she goes down 1 stair to reach stair 0.
+    *   Using an operation of the second type, she goes up 2<sup>1</sup> stairs to reach stair 2.
+    *   Using an operation of the first type, she goes down 1 stair to reach stair 1.
+
+**Constraints:**
+
+*   <code>0 <= k <= 10<sup>9</sup></code>

src/test/java/g3101_3200/s3151_special_array_i/SolutionTest.java

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+package g3101_3200.s3151_special_array_i;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+class SolutionTest {
+    @Test
+    void isArraySpecial() {
+        assertThat(new Solution().isArraySpecial(new int[] {1}), equalTo(true));
+    }
+
+    @Test
+    void isArraySpecial2() {
+        assertThat(new Solution().isArraySpecial(new int[] {2, 1, 4}), equalTo(true));
+    }
+
+    @Test
+    void isArraySpecial3() {
+        assertThat(new Solution().isArraySpecial(new int[] {4, 3, 1, 6}), equalTo(false));
+    }
+
+    @Test
+    void isArraySpecial4() {
+        assertThat(new Solution().isArraySpecial(new int[] {2, 10}), equalTo(false));
+    }
+}

src/test/java/g3101_3200/s3152_special_array_ii/SolutionTest.java

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+package g3101_3200.s3152_special_array_ii;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+class SolutionTest {
+    @Test
+    void isArraySpecial() {
+        assertThat(
+                new Solution().isArraySpecial(new int[] {3, 4, 1, 2, 6}, new int[][] {{0, 4}}),
+                equalTo(new boolean[] {false}));
+    }
+
+    @Test
+    void isArraySpecial2() {
+        assertThat(
+                new Solution().isArraySpecial(new int[] {4, 3, 1, 6}, new int[][] {{0, 2}, {2, 3}}),
+                equalTo(new boolean[] {false, true}));
+    }
+}

src/test/java/g3101_3200/s3153_sum_of_digit_differences_of_all_pairs/SolutionTest.java

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+package g3101_3200.s3153_sum_of_digit_differences_of_all_pairs;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+class SolutionTest {
+    @Test
+    void sumDigitDifferences() {
+        assertThat(new Solution().sumDigitDifferences(new int[] {13, 23, 12}), equalTo(4L));
+    }
+
+    @Test
+    void sumDigitDifferences2() {
+        assertThat(new Solution().sumDigitDifferences(new int[] {10, 10, 10, 10}), equalTo(0L));
+    }
+}

src/test/java/g3101_3200/s3154_find_number_of_ways_to_reach_the_k_th_stair/SolutionTest.java

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+package g3101_3200.s3154_find_number_of_ways_to_reach_the_k_th_stair;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+class SolutionTest {
+    @Test
+    void waysToReachStair() {
+        assertThat(new Solution().waysToReachStair(0), equalTo(2));
+    }
+
+    @Test
+    void waysToReachStair2() {
+        assertThat(new Solution().waysToReachStair(1), equalTo(4));
+    }
+}