Create 5.cpp

LeetCode-CN/5.cpp

@@ -0,0 +1,49 @@
+class Solution {
+public:
+    // dp[i][j]: string from i to j is palindromic
+    // dp[i][j]=true if dp[i+1][j-1]==true && s[i]==s[j]
+    static bool dp[1001][1001];
+
+    string longestPalindrome(string s) {
+        int sz = s.size();
+        memset(dp, false, sizeof(dp));
+
+        int max_len = -1;
+        int begin_at = -1;
+
+        for (int i = 0; i < sz - 1; i++)
+        {
+            dp[i][i] = true;
+            if (s[i] == s[i + 1])
+            {
+                dp[i][i + 1] = true;
+                max_len = 2;
+                begin_at = i;
+            }
+        }
+
+        for (int L = 3; L <= sz; L++)
+        {
+            for (int i = 0; i <= sz - L; i++)
+            {
+                if (dp[i + 1][i + L - 2] && s[i] == s[i + L - 1])
+                {
+                    dp[i][i + L - 1] = true;
+                    max_len = L;
+                    begin_at = i;
+                }
+            }
+        }
+        
+        // debug
+        // cout << begin_at << " " << max_len << endl;
+        if (max_len == -1)
+        {
+            return s.substr(0, 1);
+        }
+        return s.substr(begin_at, max_len);
+    }
+};
+
+// decl
+bool Solution::dp[1001][1001];