fd

Author: dingjikerbo

README.md

@@ -379,6 +379,7 @@
 |560|[Subarray Sum Equals K](https://leetcode.com/problems/subarray-sum-equals-k/)| [Java](leetcode/solution/src/SubarraySumEqualsK.java)|70||
 |606|[Construct String from Binary Tree](https://leetcode.com/problems/construct-string-from-binary-tree/)|[Java](leetcode/solution/src/ConstructStringFromBinaryTree.java)|90||
 |617|[Merge Two Binary Trees](https://leetcode.com/problems/merge-two-binary-trees/)|[Java](leetcode/solution/src/MergeTwoBinaryTrees.java)|100|很简单|
+|621|[Task Scheduler](https://leetcode.com/problems/task-scheduler/)|[Java](leetcode/solution/src/TaskScheduler.java)|70||
 |637|[Average of Levels in Binary Tree](https://leetcode.com/problems/average-of-levels-in-binary-tree/#/description)| [Java](leetcode/solution/src/AverageOfLevelsInBinaryTree.java)|100||
 |652|[Find Duplicate Subtrees](https://leetcode.com/problems/find-duplicate-subtrees/)| [Java](leetcode/solution/src/FindDuplicateSubtrees.java)|70|开始还没思路|
 |653|[Two Sum IV - Input is a BST](https://leetcode.com/problems/two-sum-iv-input-is-a-bst/)| [Java](leetcode/solution/src/TwoSumIV.java)|90||

leetcode/solution/src/TaskScheduler.java

@@ -0,0 +1,23 @@
+import java.util.Arrays;
+
+public class TaskScheduler {
+
+    /**
+     * 这题关键是先按频率排序，最高频的优先占座，中间隔着stub，然后依次插次低频的
+     * 有两种情况，
+     * 一种是stub不够用，元素不但给stub替换完了，还要多塞元素，如AAAABBBBCCCCDDDD, n=2，这种情况结果是tasks.length
+     * 第二种是stub太多了，元素替换不完，中间留了不少空，如AABB, n=3，这种情况结果是(count[25] - 1) * n + count[25] + 24 - i
+     * 这里(count[25] - 1) * n是插入的stub总数，24 - i是除了count[25]外和count[25]同样频率的数的个数
+     */
+    public int leastInterval(char[] tasks, int n) {
+        int[] count = new int[26];
+        for (char c : tasks) {
+            count[c - 'A']++;
+        }
+        Arrays.sort(count);
+        int i = 25;
+        for (; i >= 0 && count[i] == count[25]; i--) ;
+        // (count[25] - 1) * n + count[25] + 24 - i = (count[25] - 1) * (n + 1) + 25 - i
+        return Math.max(tasks.length, (count[25] - 1) * (n + 1) + 25 - i);
+    }
+}

leetcode/src/Main.java

@@ -4,16 +4,15 @@ public class Main {
 
     public static class Solution {
 
-        public int subarraySum(int[] nums, int k) {
-            HashMap<Integer, Integer> map = new HashMap<>();
-            map.put(0, 1);
-            int count = 0;
-            for (int i = 0, sum = 0; i < nums.length; i++) {
-                sum += nums[i];
-                map.put(sum, map.getOrDefault(sum, 0) + 1);
-                count += map.getOrDefault(sum - k, 0);
+        public int leastInterval(char[] tasks, int n) {
+            int[] count = new int[26];
+            for (char c : tasks) {
+                count[c - 'A']++;
             }
-            return count;
+            Arrays.sort(count);
+            int i = 25;
+            for ( ; i >= 0 && count[i] == count[25]; i--);
+            return Math.max(tasks.length, (count[25] - 1) * (n + 1) + 25 - i);
         }
     }