C++ Reverse Fill
Generate the initial string with all \'a\' characters. This will reduce k by n. \n    \nThen, turn rightmost \'a\' into \'z\' (\'a\' + 25, or \'a\' + k) while k
Generate the initial string with all \'a\' characters. This will reduce `k` by `n`. \n    \nThen, turn rightmost \'a\' into \'z\' (\'a\' + 25, or \'a\' + k) while `k` is positive.\n\n```cpp\nstring getSmallestString(int n, int k) {\n    string res = string(n, \'a\');\n    k -= n;\n    while (k > 0) {\n        res[--n] += min(25, k);\n        k -= min(25, k);\n    }\n    return res;\n}\n```
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