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+# [171. Excel Sheet Column Number](https://leetcode.com/problems/excel-sheet-column-number/description/)
+# 思路
+第[168题](https://leetcode.com/problems/excel-sheet-column-title/description/)是将10进制转换为26进制，这题是将26进制转换为10进制.    
+例：将k进制数"abcd"转换为10进制数：`res = d * k^0 + c * k^1 + b * k^2 + a * k^3`.
+# C++
+```
+class Solution {
+public:
+    int titleToNumber(string s) {
+        int res = 0, multiplier = 1;
+        for(int i = s.size() - 1; i >= 0; i--){
+            res += (int)(s[i] - 'A' + 1) * multiplier;
+            multiplier *= 26;
+        }
+        return res;
+    }
+};
+```