Sliding Window Median

Author: lessfish

Algorithms/Sliding Window Median/sliding-window-median.js

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+// Source : https://leetcode.com/problems/sliding-window-median/
+// Author : Han Zichi
+// Date   : 2017-01-22
+
+/**
+ * @param {number[]} nums
+ * @param {number} k
+ * @return {number[]}
+ */
+var medianSlidingWindow = function(nums, k) {
+  let ans = []
+    , res = nums.slice(0, k);
+
+  let findMedian = () => {
+    if (k & 1)
+      return res[k >> 1];
+    else {
+      let a = (k >> 1) - 1
+        , b = k >> 1;
+      return (res[a] + res[b]) / 2;
+    }
+  };
+
+  res.sort((a, b) => a - b);
+
+  ans.push(findMedian());
+
+  for (let i = k, len = nums.length; i < len; i++) {
+    let insertPos = binarySearch2(res, nums[i]);
+    res.splice(insertPos, 0, nums[i]);
+
+    let delPos = binarySearch(res, nums[i - k]);
+    res.splice(delPos, 1);
+
+    ans.push(findMedian());
+  }
+
+  return ans;
+};
+
+/**
+ * 查找有序数组中第一次出现某数的位置，如果没找到，返回 -1
+ * @param  {number[]} a      从小到大排列的有序数组
+ * @param  {number} target   需要查找的元素值
+ * @return {number}          数组下标，如果没找到，该值为 -1
+ */
+function binarySearch(a, target) {
+  var start = 0
+    , end = a.length - 1;
+
+  while (start <= end) {
+    var mid = (start + end) >> 1;
+    if (a[mid] >= target)
+      end = mid - 1;
+    else
+      start = mid + 1;
+  }
+
+  return a[start] === target ? start : -1;
+}
+
+/**
+ * 查找有序数组中刚好比某数大的元素位置，如果所有数都比该数小，则返回 a.length
+ * @param  {number[]} a      从小到大排列的有序数组
+ * @param  {number} target   需要查找的元素值
+ * @return {number}          数组下标
+ */
+function binarySearch2(a, target) {
+  target += 1;
+  var start = 0
+    , end = a.length - 1;
+
+  while (start <= end) {
+    var mid = (start + end) >> 1;
+    if (a[mid] >= target)
+      end = mid - 1;
+    else
+      start = mid + 1;
+  }
+
+  return start;
+}