求两个字符串的最长公共子串（动态规划）

向右看齐 2022-10-23 11:19 190阅读 0赞

**最长公共子串问题是寻找两个或多个已知字符串最长的子串。此问题与最长公共子序列问题的区别在于子序列不必是连续的，而子串却必须是。**

public class A {
    
    
        private static int getCommonStrLength(String str1, String str2) {
            //创建一个二维数组大小，行列为str1.length()+1，str2.length()
            //这一步主要是为了生成网格数组
            int len1 = str1.length();
            int len2 = str2.length();
            int[][] dp = new int[len1 + 1][len2 + 1];
    
            //核心/填充网格数组
            for (int i = 1; i <= len1; i++) {
                for (int j = 1; j <= len2; j++) {
                    //如果两个字符相等，那么就获取dp[i - 1][j - 1]该位置的网格的值且加一
                    if (str1.charAt(i - 1) == str2.charAt(j - 1)) {
                        dp[i][j] = dp[i - 1][j - 1] + 1;
                    } else {
                        //说明不相等
                        dp[i][j] = 0;
                    }
                }
            }
            //找到最大值和下标
            int max = 0;
            int max_y = 0;
            for (int i = 0; i <= len1; i++) {
                for (int j = 0; j <= len2; j++) {
                    if (dp[i][j] > max) {
                        max = dp[i][j];
                        max_y = j;
                    }
                }
            }
            System.out.println(str2.substring(max_y  - max, max_y ));
            return max;
        }
    
    
        public static void main(String[] args) {
            System.out.println(getCommonStrLength("1234", "123456"));
        }
    
    
    }

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