update

src/动态规划/q1143_最长公共子序列/Solution.java

@@ -2,7 +2,7 @@ package 动态规划.q1143_最长公共子序列;
 
 /**
  * 动态规划 dp[i + 1][j + 1] = Math.max(dp[i+1][j], dp[i][j+1]) o(m*n)
- *
+ * <p>
  * 若题目为最长公共子串，则在c1,c2不相等时不做处理（赋值0），在遍历过程中记录最大值即可
  */
 public class Solution {
@@ -25,4 +25,37 @@ public class Solution {
         }
         return dp[m][n];
     }
+
+    /**
+     * 最长公共字串
+     *
+     * @param str1
+     * @param str2
+     * @return
+     */
+    public static String longestCommonSubstring(String str1, String str2) {
+        int m = str1.length();
+        int n = str2.length();
+        int[][] dp = new int[m + 1][n + 1];
+        int maxLength = 0;
+        int endIndex = -1;
+
+        for (int i = 1; i <= m; i++) {
+            for (int j = 1; j <= n; j++) {
+                if (str1.charAt(i - 1) == str2.charAt(j - 1)) {
+                    dp[i][j] = dp[i - 1][j - 1] + 1;
+                    if (dp[i][j] > maxLength) {
+                        maxLength = dp[i][j];
+                        endIndex = i - 1;
+                    }
+                } else {
+                    dp[i][j] = 0;
+                }
+            }
+        }
+        if (maxLength == 0) {
+            return "";
+        }
+        return str1.substring(endIndex - maxLength + 1, endIndex + 1);
+    }
 }