最长公共子序列

定义dp[i][j]为a中前i个与b中前j个能匹配的最大长度

当 a[i] == b[j] 时，答案来自 dp[i - 1][j - 1] + 1

否则，来自dp[i - 1][j]与dp[i][j-1]中较大一个

for(rint i = 1;i <= n; ++i) {
        for(rint j = 1;j <= m; ++j) {
            if(a[i] == b[j]) dp[i][j] = dp[i - 1][j - 1] + 1;
            else dp[i][j] = max(dp[i - 1][j],dp[i][j - 1]);
        }
    } 

来源：https://www.cnblogs.com/Thomastine/p/11729351.html