3474. Lexicographically Smallest Generated String

2026-04-01 11:28:34 +03:00
parent 3b9bbfe3db
commit 3d490d6027
4 changed files with 121 additions and 0 deletions
--- a/String/Solution.cs
+++ b/String/Solution.cs
@@ -0,0 +1,87 @@
+using System.Text;
+
+public class Solution
+{
+    public string GenerateString(string str1, string str2)
+    {
+        var len = str1.Length + str2.Length - 1;
+        var answer = new char[len];
+
+        // Сначала обработать все T
+        for (var i = 0; i < str1.Length; i++)
+        {
+            if (str1[i] == 'T')
+            {
+                var sbIdx = i;
+                for (var j = 0; j < str2.Length; j++)
+                {
+                    if (answer[sbIdx] != 0 && answer[sbIdx] != str2[j])
+                        return "";
+                    answer[sbIdx++] = str2[j];
+                }
+            }
+        }
+        // Теперь обработать все F
+        var canChange = new bool[len];
+        var lastF = -1;
+        for (var i = 0; i < str1.Length; i++)
+            if (str1[i] == 'F')
+            {
+                if (ProcessF(answer.AsSpan()[i..(i + str2.Length)], str2, canChange.AsSpan()[i..(i + str2.Length)], out var goBack) == false)
+                    return "";
+                if(goBack && lastF != -1) 
+                    i = lastF - 1;
+                else
+                    lastF = i;
+            }
+
+        return new string(answer);
+    }
+
+    private bool ProcessF(Span<char> chars, string s2, Span<bool> canChange, out bool goBack)
+    {
+        goBack = false;
+
+        var equal = true;
+        var emptyCount = 0;
+        var hasDiff = false;
+        var lastCanChange = -1;
+        for (var i = 0; i < s2.Length; i++)
+        {
+            equal &= chars[i] == s2[i];
+            if (chars[i] == 0)
+                emptyCount++;
+            else if (chars[i] != s2[i])
+                hasDiff = true;
+            if (canChange[i])
+                lastCanChange = i;
+        }
+        if (equal)
+        {
+            if (lastCanChange >= 0)
+            {
+                chars[lastCanChange]++;
+                if (chars[lastCanChange] == 'z' + 1)
+                    chars[lastCanChange] = 'a';
+                goBack = true;
+                return true;
+            }
+            else
+                return false;
+        }
+        for (var i = 0; i < chars.Length && emptyCount > 0; i++)
+        {
+            if (chars[i] != 0)
+                continue;
+            var insert = 'a';
+            if (emptyCount == 1 && s2[i] == insert && !hasDiff)
+                insert++;
+            chars[i] = insert;
+            canChange[i] = true;
+            if (s2[i] != insert)
+                hasDiff = true;
+            emptyCount--;
+        }
+        return true;
+    }
+}