2020.9.17

14.最长公共前缀.java

@@ -0,0 +1,44 @@
+/*
+ * @lc app=leetcode.cn id=14 lang=java
+ *
+ * [14] 最长公共前缀
+ */
+
+// @lc code=start
+class Solution {
+    public String longestCommonPrefix(String[] strs) {
+       // StringBuilder ans = new StringBuilder();
+        if(strs.length == 1){
+            return strs[0];
+        }
+        if(strs.length == 0){
+            return "";
+        }
+        String index = strs[0];
+        for(int i=1;i<strs.length - 1;i++){
+            if(index.length() > strs[i].length()){
+                index = strs[i];
+            }            
+        }
+        int flag = 0;
+        while(index.length() > 0){
+            for(int i = 0;i<strs.length;i++){
+                if(strs[i].startsWith(index)){
+                    flag = 1;
+                    continue;
+                }else{
+                    flag = 0;
+                    break;
+                }
+            }
+            if(flag == 1){
+                return index;
+            }else{
+                index = index.substring(0, index.length() - 1);
+            }
+        }
+        return "";
+    }
+}
+// @lc code=end
+

15.三数之和.java

@@ -0,0 +1,54 @@
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+/*
+ * @lc app=leetcode.cn id=15 lang=java
+ *
+ * [15] 三数之和
+ */
+
+// @lc code=start
+class Solution {
+    public List<List<Integer>> threeSum(int[] nums) {
+        List<List<Integer>> ans = new ArrayList<>();
+
+        if(nums == null || nums.length < 3){
+            return ans;
+        }
+
+        Arrays.sort(nums);
+
+        if(nums[0]> 0){
+            return ans;
+        }
+        int start,end = 0;
+        for(int i = 0;i<nums.length - 2;i++){
+            if(i > 0 && (nums[i] == nums[i - 1])){
+                continue;
+            }
+            start = i + 1;
+            end = nums.length -1;
+            while(start < end){
+                if(nums[i] + nums[start] + nums[end] == 0){
+                    ans.add(new ArrayList<>(Arrays.asList(nums[i],nums[start],nums[end])));
+                    start++;
+                    end--;
+                    while(start < end && nums[start] == nums[start - 1]){
+                        start++;
+                    }
+                    while(start < end && nums[end] == nums[end + 1]){
+                        end--;
+                    }
+                }else if(nums[i] + nums[start] + nums[end] < 0){
+                    start++;
+                }else if(nums[i] + nums[start] + nums[end] > 0){
+                    end--;
+                }
+            }
+        }
+        return ans;
+    }
+}
+// @lc code=end
+