题目大意：输入A，B字符串，A由a1，a2...an字符组成，B由b1，b2...bn字符组成。求最长公共子序列。
解题思路：dp二维数组，dp[i][j]表示，a1，a2..ai与b1，b2...bj最长公共子序列。如果ai等于bj，dp[i][j] = dp[i-1][j-1] + 1;否则dp[i][j] = max(dp[i-1][j], dp[i][j-1]);
ac代码：
#include <iostream>
#include <cstring>
using namespace std;
int dp[1005][1005], len1, len2;
char a[1005], b[1005];
int main()
{ while (scanf("%s%s", a, b)!=EOF){len1 = strlen(a), len2 = strlen(b);memset(dp, 0, sizeof(dp));for (int i=1; i<=len1; i++)for (int j=1; j<=len2; j++)if (a[i-1] == b[j-1])dp[i][j] = dp[i-1][j-1] + 1;elsedp[i][j] = max(dp[i-1][j], dp[i][j-1]);printf("%d\n", dp[len1][len2]);}return 0;
}