两道微小的题

Author: YorkPeng

1143.最长公共子序列.java

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+/*
+ * @lc app=leetcode.cn id=1143 lang=java
+ *
+ * [1143] 最长公共子序列
+ */
+
+// @lc code=start
+class Solution {
+    public int longestCommonSubsequence(String text1, String text2) {
+        if(text1 == null || text1.length() == 0 || text2 == null || text2.length() == 0){
+            return 0;
+        }
+        char[] str1 = text1.toCharArray();
+        char[] str2 = text2.toCharArray();
+        int n = str1.length;
+        int m = str2.length;
+        int[][] dp = new int[n][m];
+        dp[0][0] = str1[0] == str2[0]?1:0;
+        for(int i = 1;i<n;i++){
+            dp[i][0] = str1[i] == str2[0]?1:dp[i-1][0];
+        }
+        for(int i = 1;i<m;i++){
+            dp[0][i] = str1[0] == str2[i]?1:dp[0][i-1];
+        }
+        for(int i = 1; i < n;i++){
+            for(int j = 1;j<m;j++){
+                if(str1[i] == str2[j]){
+                    dp[i][j] = Math.max(dp[i][j],dp[i-1][j-1]+1);
+                }else{
+                    dp[i][j] = Math.max(dp[i-1][j],dp[i][j-1]);
+                }
+            }
+        }
+        return dp[n-1][m-1];
+    }
+}
+// @lc code=end
+

200.岛屿数量.java

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+/*
+ * @lc app=leetcode.cn id=200 lang=java
+ *
+ * [200] 岛屿数量
+ */
+
+// @lc code=start
+class Solution {
+    public int numIslands(char[][] grid) {
+        int count = 0;
+        for(int i =0; i < grid.length;i++){
+            for(int j = 0; j < grid[i].length;j++){
+                if(grid[i][j] == '1'){
+                    dfs(grid, i, j);
+                    count++;
+                }
+            }
+        }
+        return count;
+    }
+
+    private void dfs(char[][] grid, int i, int j){
+        int n = grid.length;
+        int m = grid[n].length;
+        if(i < 0 || j<0 || i >=n||j>=m){
+            return;
+        }
+        if(grid[i][j] == '0' || grid[i][j] == '2'){
+            return;
+        }
+        grid[i][j] = '2';
+        dfs(grid, i, j-1);
+        dfs(grid, i, j+1);
+        dfs(grid, i-1, j);
+        dfs(grid, i+1, j);
+    }
+}
+// @lc code=end
+