最长公共子序列(dp)

class Solution {
public:
	int longestCommonSubsequence(string a, string b) {
		int n = a.size();
		int m = b.size();
		vevtor<vector<int>> f(n+1, vector<int>(m+1, 0));
		for (int i=1; i<=n; ++i) {
			for (int j=1; j<=m; ++j) {
				f[i][j] = max(f[i-1][j], f[i][j-1]);
				if (a[i-1] == b[j-1]) {
					f[i][j] = max(f[i-1][j-1]+1, f[i][j]);
				}
			}
		}
		return f[n][m];
	}
};