LintCode: Longest Common Substring

C++

暴力搜索

两个游标一个长度

i遍历a

j遍历b

len遍历公共子串长度

class Solution {
public:    
    /**
     * @param A, B: Two string.
     * @return: the length of the longest common substring.
     */
    int longestCommonSubstring(string &A, string &B) {
        // write your code here
        int m = A.size();
        int n = B.size();
        if (m == 0 || n == 0) {
            return 0;
        }
        int ans = 0;
        for (int i = 0; i < m; ++i) {
            for (int j = 0; j < n; ++j) {
                int len = 0;
                while (i + len < m && j + len < n && A[i + len] == B[j + len]) {
                    len ++;
                    ans = max(ans, len);
                }
            }
        }
        return ans;
    }
};

C++,

dp

class Solution {
public:    
    /**
     * @param A, B: Two string.
     * @return: the length of the longest common substring.
     */
    int longestCommonSubstring(string &A, string &B) {
        // write your code here
        int m = A.size();
        int n = B.size();
        if (m == 0 || n == 0) {
            return 0;
        }
        vector<vector <int> > dp(m + 1, vector<int>(n + 1));
        // int[][] dp = new int[m + 1][n + 1];
        int ans = 0;
        for (int i = 0; i <= m; ++i) {
            for (int j = 0; j <= n; ++j) {
                if (i == 0 || j == 0) {
                    dp[i][j] = 0;
                } else {
                    if (A[i-1] == B[j-1]) {
                        dp[i][j] = dp[i - 1][j - 1] + 1;
                        ans = max(dp[i][j], ans);
                    } else {
                        dp[i][j] = 0;
                    }
                }
            }
        }
        return ans;
    }
};