#feat:leetcode p287题题解

src/leetcode/p287/Solution.java

@@ -0,0 +1,60 @@
+package leetcode.p287;
+
+import java.util.HashMap;
+
+/**
+ * @ProjectName: LeetCode
+ * @FileName: Solution
+ * @Author: 杨逸
+ * @Data:2026/3/3 19:50
+ * @Description: https://leetcode.cn/problems/find-the-duplicate-number/?envType=study-plan-v2&envId=top-100-liked
+ * 287. 寻找重复数
+ */
+public class Solution {
+    /**
+     * @param nums
+     * @return
+     */
+    public int findDuplicate(int[] nums) {
+        return firstMissingPositive(nums);
+    }
+    private int hashMapSolution(int[] nums){
+        HashMap<Integer, Integer> map = new HashMap<>();
+        for (int num : nums) {
+            Integer count = map.getOrDefault(num, 0);
+            if (count!=0) {
+                return num;
+            }
+            map.put(num,count+1);
+        }
+        return 0;
+    }
+
+    /**
+     * 参考第一个缺失正整数的解法
+     * 假设:数字1应该储存在nums[0],数字2应该储存在nums[1]...
+     * 将数组调整为符合假设的状态,因为只有一个正整数重复,且nums都是正数,所以重复的数字就是调整后不在合法的位置
+     * 该解法会修改原数组,不满题目要求,但是可以解
+     * @param nums
+     * @return
+     */
+    private int firstMissingPositive(int[] nums){
+        int index = 0;
+        while (index < nums.length){
+            if (nums[index] > 0 && nums[index] <= nums.length){
+                int temp = nums[index];
+                //如果nums[index]已经在正确的位置上,则跳过
+                if (nums[index] == nums[temp-1]){
+                    index++;
+                    continue;
+                }
+                //将nums[index]放到符合设定的位置
+                nums[index] = nums[temp-1];
+                nums[temp-1] = temp;
+            }else{
+                index++;
+            }
+        }
+        return nums[nums.length - 1];
+    }
+}

src/leetcode/p287/SolutionTest.java

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+package leetcode.p287;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+/**
+ * @ProjectName: LeetCode
+ * @FileName: SolutionTest
+ * @Author: 杨逸
+ * @Data:2026/3/3 19:53
+ * @Description:
+ */
+public class SolutionTest {
+
+    @Test
+    public void findDuplicate() {
+        Solution solution = new Solution();
+        int[] nums = new int[]{1,3,4,2,2};
+        int result = solution.findDuplicate(nums);
+        assertEquals(2,result);
+        nums = new int[]{3,3,3,3,3};
+        result = solution.findDuplicate(nums);
+        assertEquals(3,result);
+    }
+}