New Problem "Excel Sheet Column Title"

Author: haoel

src/excelSheetColumnTitle/excelSheetColumnTitle.cpp

@@ -0,0 +1,72 @@
+// Source : https://oj.leetcode.com/problems/excel-sheet-column-title/
+// Author : Hao Chen
+// Date   : 2014-12-25
+
+/********************************************************************************** 
+ * 
+ * Given a positive integer, return its corresponding column title as appear in an Excel sheet.
+ * 
+ * For example:
+ * 
+ *     1 -> A
+ *     2 -> B
+ *     3 -> C
+ *     ...
+ *     26 -> Z
+ *     27 -> AA
+ *     28 -> AB 
+ * 
+ * Credits:Special thanks to @ifanchu for adding this problem and creating all test cases.
+ *               
+ **********************************************************************************/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <iostream>
+#include <string>
+using namespace std;
+
+
+string base26_int2str(long long n) {
+    string ret;
+    while(n>0){
+        char ch = 'A' + (n-1)%26;
+        ret.insert(ret.begin(), ch  );
+        n -= (n-1)%26;
+        n /= 26;
+    }
+    return ret;
+}
+
+long long base26_str2int(string& s){
+    long long ret=0;
+    for (int i=0; i<s.size(); i++){
+        int n = s[i] - 'A' + 1;
+        ret = ret*26 + n;
+    }
+    return ret;
+}
+
+
+string convertToTitle(int n) {
+    return base26_int2str(n);
+}
+
+int main(int argc, char**argv)
+{
+    long long n = 27; 
+    if (argc>1){
+        n = atoll(argv[1]);
+    }
+    string ns = base26_int2str(n);
+    n = base26_str2int(ns);
+
+    cout << n << " = " << ns << endl;
+
+
+    ns = "ABCDEFG";
+    if (argc>2){
+        ns = argv[2];
+    }
+    cout << ns << " = " << base26_str2int(ns) << endl;
+}