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+/*
+Challenge 241
+
+Task 1: Arithmetic Triplets
+Submitted by: Mohammad S Anwar
+
+You are given an array (3 or more members) of integers in increasing order
+and a positive integer.
+
+Write a script to find out the number of unique Arithmetic Triplets satisfying
+the following rules:
+
+a) i < j < k
+b) nums[j] - nums[i] == diff
+c) nums[k] - nums[j] == diff
+
+Example 1
+
+Input: @nums = (0, 1, 4, 6, 7, 10)
+       $diff = 3
+Output: 2
+
+Index (1, 2, 4) is an arithmetic triplet because both  7 - 4 == 3 and 4 - 1 == 3.
+Index (2, 4, 5) is an arithmetic triplet because both 10 - 7 == 3 and 7 - 4 == 3.
+
+Example 2
+
+Input: @nums = (4, 5, 6, 7, 8, 9)
+       $diff = 2
+Output: 2
+
+(0, 2, 4) is an arithmetic triplet because both 8 - 6 == 2 and 6 - 4 == 2.
+(1, 3, 5) is an arithmetic triplet because both 9 - 7 == 2 and 7 - 5 == 2.
+*/
+
+#include <iostream>
+#include <string>
+#include <vector>
+using namespace std;
+
+int count_triplets(vector<int>& nums, int diff) {
+    int count = 0;
+    for (int i = 0; i < static_cast<int>(nums.size()) - 2; i++) {
+        for (int j = i + 1; j < static_cast<int>(nums.size()) - 1; j++) {
+            for (int k = j + 1; k < static_cast<int>(nums.size()); k++) {
+                if (nums[j] - nums[i] == diff && nums[k] - nums[j] == diff)
+                    count++;
+            }
+        }
+    }
+    return count;
+}
+
+void usage(void) {
+    cerr << "Usage: ch-1 -nums n n n ... -diff n" << endl;
+    exit(EXIT_FAILURE);
+}
+
+int main(int argc, char* argv[]) {
+    vector<int> nums;
+    int diff = -1;
+
+    // parse args
+    int i = 1;
+    while (i < argc) {
+        string arg = argv[i];
+        if (arg == "-nums") {
+            i++;
+            while (i < argc && argv[i][0] != '-') {
+                int n = atoi(argv[i]);
+                nums.push_back(n);
+                i++;
+            }
+        }
+        else if (arg == "-diff") {
+            i++;
+            if (i < argc) {
+                diff = atoi(argv[i]);
+                i++;
+            }
+        }
+        else {
+            usage();
+        }
+    }
+    if (nums.empty() || diff < 0)
+        usage();
+
+    // process
+    int count = count_triplets(nums, diff);
+    cout << count << endl;
+}