add javascript counting sort

javascript/13_sorts/countingSort.js

@@ -0,0 +1,38 @@
+const countingSort = array => {
+    if (array.length <= 1) return
+
+    const max = findMaxValue(array)
+    const counts = new Array(max + 1)
+
+    // 计算每个元素的个数，放入到counts桶中
+    // counts下标是元素，值是元素个数
+    array.forEach(element => {
+        if (!counts[element]) {
+            counts[element] = 0
+        }
+        counts[element]++
+    })
+
+    // counts下标是元素，值是元素个数
+    // 例如： array: [6, 4, 3, 1], counts: [empty, 1, empty, 1, 1, empty, 1]
+    // i是元素, count是元素个数
+    let sortedIndex = 0
+    counts.forEach((count, i) => {
+        while (count > 0) {
+            array[sortedIndex] = i
+            sortedIndex++
+            count--
+        }
+    })
+    // return array
+}
+
+function findMaxValue(array) {
+    let max = array[0]
+    for (let i = 1; i < array.length; i++) {
+        if (array[i] > max) {
+            max = array[i]
+        }
+    }
+    return max
+}