leetcode

commit b625f10863beea22bfd39f94a1858c0d85e0f355
parent c5bd23a3622d190bd4bc63030a2216bed6055886
Author: Jack Sangdahl <jack@pngu.org>
Date:   Mon, 10 Nov 2025 11:00:46 -0700

784. letter case permutation

Diffstat:
A
letter_case_permutation.c
 | 
61
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
A
letter_case_permutation.py
 | 
23
+++++++++++++++++++++++

2 files changed, 84 insertions(+), 0 deletions(-)
diff --git a/letter_case_permutation.c b/letter_case_permutation.c
@@ -0,0 +1,61 @@
+// 784. Letter Case Permutation
+#include "leetcode.h"
+
+/*
+ * given a string 's', you can transform every letter individually to be
+ * lowercase or uppercase. return a list of all possible strings we could
+ * create. return the output in any order.
+ */
+
+void helper(char *s, int n, int j, char **res, int *cnt, char *str) {
+  if (j == n) {
+    char *tmp = (char *)malloc((n + 1) * sizeof(char));
+    memcpy(tmp, str, n);
+    tmp[n] = '\0';
+    res[(*cnt)++] = tmp;
+    return;
+  }
+  char c1 = *(s + j);
+  if (!(c1 >= '0' && c1 <= '9')) {
+    char c2 = c1 >= 'a' ? c1 - ('a' - 'A') : c1 + ('a' - 'A');
+    str[j] = c2;
+    helper(s, n, j + 1, res, cnt, str);
+  }
+  str[j] = c1;
+  helper(s, n, j + 1, res, cnt, str);
+}
+
+char **letterCasePermutation(char *s, int *returnSize) {
+  char *perm = s;
+  int total = 1, n = 0, cnt = 0;
+  while (*perm) {
+    if (!(*perm >= '0' && *perm <= '9'))
+      total *= 2;
+    perm++;
+    n++;
+  }
+  char **ans = (char **)malloc(total * sizeof(char *));
+  char *str = malloc((n + 1) * sizeof(char));
+  helper(s, n, 0, ans, &cnt, str);
+  *returnSize = total;
+  return ans;
+}
+
+int main() {
+  char *s1 = "a1b2", *s2 = "3z4";
+  int rs1, rs2;
+  char **lcp1 = letterCasePermutation(s1, &rs1);
+  char **lcp2 = letterCasePermutation(s2, &rs2);
+  for (int i = 0; i < rs1; i++)
+    printf("%s ", lcp1[i]); // expect: ["a1b2","a1B2","A1b2","A1B2"]
+  printf("\n");
+  for (int i = 0; i < rs2; i++)
+    printf("%s ", lcp2[i]); // expect: ["3z4","3Z4"]
+  printf("\n");
+  for (int i = 0; i < rs1; i++)
+    free(lcp1[i]);
+  free(lcp1);
+  for (int i = 0; i < rs2; i++)
+    free(lcp2[i]);
+  free(lcp2);
+}
diff --git a/letter_case_permutation.py b/letter_case_permutation.py
@@ -0,0 +1,23 @@
+# 784. Letter Case Permutation
+from itertools import product
+
+"""
+given a string 's', you can transform every letter individually to be
+lowercase or uppercase. return a list of all possible strings we could
+create. return the output in any order.
+"""
+
+
+class Solution(object):
+    def letterCasePermutation(self, s):
+        """
+        :type s: str
+        :rtype: List[str]
+        """
+        return map("".join, product(*[set([i.lower(), i.upper()]) for i in s]))
+
+
+if __name__ == "__main__":
+    obj = Solution()
+    print(obj.letterCasePermutation(s="a1b2"))
+    print(obj.letterCasePermutation(s="3z4"))