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+/*
+Challenge 245
+
+Task 2: Largest of Three
+Submitted by: Mohammad S Anwar
+
+You are given an array of integers >= 0.
+
+Write a script to return the largest number formed by concatenating some of
+the given integers in any order which is also multiple of 3. Return -1 if
+none found.
+
+Example 1
+
+Input: @ints = (8, 1, 9)
+Output: 981
+
+981 % 3 == 0
+
+Example 2
+
+Input: @ints = (8, 6, 7, 1, 0)
+Output: 8760
+
+Example 3
+
+Input: @ints = (1)
+Output: -1
+*/
+
+#include <iostream>
+#include <vector>
+using namespace std;
+
+int calc_largest(int prefix, const vector<int>& nums) {
+    int largest = -1;
+
+    // check current prefix
+    if (prefix != 0 && prefix % 3 == 0 && prefix > largest)
+        largest = prefix;
+
+    // check all compinations of each number in nums
+    vector<int> remain;
+    for (size_t i = 0; i < nums.size(); i++) {
+        // create list of numbers excluding n
+        int n = nums[i];
+        remain = nums;
+        remain.erase(remain.begin() + i);
+
+        int this_largest = calc_largest(prefix * 10 + n, remain);
+        if (this_largest > largest)
+            largest = this_largest;
+    }
+
+    return largest;
+}
+
+int main(int argc, char* argv[]) {
+    if (argc < 2) {
+        cerr << "Usage: ch-2 n n n..." << endl;
+        exit(EXIT_FAILURE);
+    }
+
+    vector<int> nums;
+    for (int i = 1; i < argc; i++)
+        nums.push_back(atoi(argv[i]));
+
+    int largest = calc_largest(0, nums);
+    cout << largest << endl;
+}