lc171.Excel表列序号

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class Solution {
public:
    int titleToNumber(string columnTitle) {
        // 正向遍历->叠加权重
        int ans = 0, n = columnTitle.size();

        for(int i = 0; i < n; i++){
            ans = columnTitle[i] - 'A' + ans * 26 + 1;
        }

        return ans;
    }
};

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class Solution {
public:
    int titleToNumber(string columnTitle) {
        // 反向->计算位权重
        int ans = 0, n = columnTitle.size();
        long long weight = 1;
        for(int i = n - 1; i >= 0; i--){
            ans += (columnTitle[i] - 'A' + 1) * weight;
            weight *= 26;
        }

        return ans;
    }
};