feat: add question 215

Author: yinxin630

215.data

@@ -0,0 +1,2 @@
+[3,2,3,1,2,4,5,5,6]
+4

215.数组中的第k个最大元素.js

@@ -0,0 +1,75 @@
+/*
+ * @lc app=leetcode.cn id=215 lang=javascript
+ *
+ * [215] 数组中的第K个最大元素
+ * 
+ * 1. 使用容量为 k 的最小堆
+ * 2. 最终堆内就是最大的 k 个数字, 堆顶就是结果
+ */
+
+// @lc code=start
+/**
+ * @param {number[]} nums
+ * @param {number} k
+ * @return {number}
+ */
+var findKthLargest = function(nums, k) {
+    const heap = [];
+
+    for (const n of nums) {
+        if (heap.length === k) {
+            if (n < heap[0]) {
+                continue;
+            }
+
+            heap[0] = heap[heap.length - 1];
+            heap.pop();
+
+            let i = 0;
+            while (i < heap.length) {
+                let next = i;
+                
+                if (heap[i * 2 + 1] && heap[i * 2 + 1] < heap[next]) {
+                    next = i * 2 + 1;
+                }
+                if (heap[i * 2 + 2] && heap[i * 2 + 2] < heap[next]) {
+                    next = i * 2 + 2;
+                }
+
+                if (i === next) {
+                    break;
+                }
+
+                const t = heap[i];
+                heap[i] = heap[next];
+                heap[next] = t;
+                i = next;
+            }
+        }
+
+        heap[heap.length] = n;
+
+        let i = heap.length - 1;
+        while (i > 0) {
+            let next = Math.floor((i - 1) / 2);
+            if (heap[next] < heap[i]) {
+                break;
+            }
+
+            const t = heap[i];
+            heap[i] = heap[next];
+            heap[next] = t;
+            i = next;
+        }
+    }
+
+    return heap[0];
+};
+
+// var findKthLargest = function(nums, k) {
+//     nums.sort((a, b) => b - a);
+//     return nums[k - 1];
+// };
+
+// @lc code=end
+