LeetCode #1143. Longest Common Subsequence

题目描述：

Given two strings text1 and text2, return the length of their longest common subsequence.

A subsequence of a string is a new string generated from the original string with some characters(can be none) deleted without changing the relative order of the remaining characters. (eg, "ace" is a subsequence of "abcde" while "aec" is not). A common subsequence of two strings is a subsequence that is common to both strings.

 

If there is no common subsequence, return 0.

Example 1:

Input: text1 = "abcde", text2 = "ace" 
Output: 3  
Explanation: The longest common subsequence is "ace" and its length is 3.

Example 2:

Input: text1 = "abc", text2 = "abc"
Output: 3
Explanation: The longest common subsequence is "abc" and its length is 3.

Example 3:

Input: text1 = "abc", text2 = "def"
Output: 0
Explanation: There is no such common subsequence, so the result is 0.

Constraints:

• 1 <= text1.length <= 1000
• 1 <= text2.length <= 1000
• The input strings consist of lowercase English characters only.

class Solution {
public:
    int longestCommonSubsequence(string text1, string text2) {
        text1=" "+text1, text2=" "+text2;
        int m=text1.length(),n=text2.length();
        vector<vector<int>> dp(m,vector<int>(n,0));
        // dp[i][j]表示text1[0:i]和text2[0:j]的最长公共子序列的长度
        for (int i=1;i<m;i++)
        {
            for (int j=1;j<n;j++) 
            {
                if (text1[i]==text2[j])
                    dp[i][j]=max(dp[i-1][j-1]+1,max(dp[i-1][j],dp[i][j-1]));
                else dp[i][j]=max(dp[i-1][j],dp[i][j-1]);
            }
        }
        return dp[m-1][n-1];
    }
};