foundkey

string getLongestCommonSubString(string a, string b)
{
    /* 
    dp[i, j] 为a[0, i - 1] 与 b[0, j - 1]末尾连续相等元素的数量

    dp[i, j] = 0                        (a[i] != b[j])
    dp[i, j] = dp[i - 1, j - 1] + 1     (a[i] == b[j])
    */
    vector<vector<int>> dp(a.length() + 1, vector<int>(b.length() + 1, 0));
    int index = 0;