🟢 Port problem 1920 (Build Array from Permutation) from Swift to C++23

solutions/1901-2000/1920-build-array-from-permutation/README.md

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+# 1920. Build Array from Permutation
+
+[LeetCode problem 1920](https://leetcode.com/problems/build-array-from-permutation/)
+
+- **Difficulty**: Easy
+- **Tags**: array, simulation
+
+## Description
+
+Given a zero-indexed permutation `nums`, build an array `ans` where
+`ans[i] == nums[nums[i]]` for every `i`.

solutions/1901-2000/1920-build-array-from-permutation/solution.cpp

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+#include "solution.hpp"
+
+#include <iterator>
+
+namespace leetcode::p1920 {
+
+std::vector<int> solve(const std::vector<int>& nums) {
+    std::vector<int> result;
+    result.reserve(nums.size());
+
+    for (int i = 0; i < std::ssize(nums); ++i) {
+        result.push_back(nums.at(static_cast<std::size_t>(nums.at(static_cast<std::size_t>(i)))));
+    }
+
+    return result;
+}
+
+} // namespace leetcode::p1920

solutions/1901-2000/1920-build-array-from-permutation/solution.hpp

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+#pragma once
+
+#include <vector>
+
+namespace leetcode::p1920 {
+
+// optimized: O(n) time, O(n) space — direct lookup, nums[nums[i]].
+std::vector<int> solve(const std::vector<int>& nums);
+
+} // namespace leetcode::p1920

solutions/1901-2000/1920-build-array-from-permutation/test.cpp

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+#include <catch2/catch_test_macros.hpp>
+
+#include "solution.hpp"
+
+TEST_CASE("Problem 1920", "[p1920]") {
+    CHECK(leetcode::p1920::solve({0, 2, 1, 5, 3, 4}) == std::vector<int>{0, 1, 2, 4, 5, 3});
+    CHECK(leetcode::p1920::solve({5, 0, 1, 2, 3, 4}) == std::vector<int>{4, 5, 0, 1, 2, 3});
+}