463 岛屿的周长

problems/0005.最长回文子串.md

@@ -263,21 +263,38 @@ public:
 Java：
 
 ```java
-public int[] twoSum(int[] nums, int target) {
-    int[] res = new int[2];
-    if(nums == null || nums.length == 0){
-        return res;
-    }
-    Map<Integer, Integer> map = new HashMap<>();
-    for(int i = 0; i < nums.length; i++){
-        int temp = target - nums[i];
-        if(map.containsKey(temp)){
-            res[1] = i;
-            res[0] = map.get(temp);
+// 双指针 动态规划
+class Solution {
+    public String longestPalindrome(String s) {
+        if (s.length() == 0 || s.length() == 1) return s;
+        int length = 1;
+        int index = 0;
+        boolean[][] palindrome = new boolean[s.length()][s.length()];
+        for (int i = 0; i < s.length(); i++) {
+            palindrome[i][i] = true;
+        }
+
+        for (int L = 2; L <= s.length(); L++) {
+            for (int i = 0; i < s.length(); i++) {
+                int j = i + L - 1;
+                if (j >= s.length()) break;
+                if (s.charAt(i) != s.charAt(j)) {
+                    palindrome[i][j] = false;
+                } else {
+                    if (j - i < 3) {
+                        palindrome[i][j] = true;
+                    } else {
+                        palindrome[i][j] = palindrome[i + 1][j - 1];
+                    }
+                }
+                if (palindrome[i][j] && j - i + 1 > length) {
+                    length = j - i + 1;
+                    index = i;
+                }
+            }
         }
-        map.put(nums[i], i);
+        return s.substring(index, index + length);
     }
-    return res;
 }
 ```
 

problems/0463.岛屿的周长.md

@@ -118,6 +118,27 @@ class Solution {
         return res;
     }
 }
+
+// 解法二
+class Solution {
+    public int islandPerimeter(int[][] grid) {
+        // 计算岛屿的周长 
+        // 方法二 : 遇到相邻的陆地总周长就-2
+        int landSum = 0; // 陆地数量 
+        int cover = 0; // 相邻陆地数量
+        for (int i = 0; i < grid.length; i++) {
+            for (int j = 0; j < grid[0].length; j++) {
+                if (grid[i][j] == 1) {
+                    landSum++;
+                    // 统计上面和左边的相邻陆地
+                    if(i - 1 >= 0 && grid[i-1][j] == 1) cover++;
+                    if(j - 1 >= 0 && grid[i][j-1] == 1) cover++;
+                }
+            }
+        }
+        return landSum * 4 - cover * 2;
+    }
+}
 ```
 
 Python：