新增34.朴实无华的二分查找 JavaScript版本

problems/0034.在排序数组中查找元素的第一个和最后一个位置.md

@@ -396,6 +396,46 @@ class Solution:
 ## JavaScript
 
 ```js
+var searchRange = function(nums, target) {
+    const getLeftBorder = (nums, target) => {
+        let left = 0, right = nums.length - 1;
+        let leftBorder = -2;// 记录一下leftBorder没有被赋值的情况
+        while(left <= right){
+            let middle = left + ((right - left) >> 1);
+            if(nums[middle] >= target){ // 寻找左边界，nums[middle] == target的时候更新right
+                right = middle - 1;
+                leftBorder = right;
+            } else {
+                left = middle + 1;
+            }
+        }
+        return leftBorder;
+    }
+
+    const getRightBorder = (nums, target) => {
+        let left = 0, right = nums.length - 1;
+        let rightBorder = -2; // 记录一下rightBorder没有被赋值的情况
+        while (left <= right) {
+            let middle = left + ((right - left) >> 1);
+            if (nums[middle] > target) {
+                right = middle - 1;
+            } else { // 寻找右边界，nums[middle] == target的时候更新left
+                left = middle + 1;
+                rightBorder = left;
+            }
+        }
+        return rightBorder;
+    }
+
+    let leftBorder = getLeftBorder(nums, target);
+    let rightBorder = getRightBorder(nums, target);
+    // 情况一
+    if(leftBorder === -2 || rightBorder === -2) return [-1,-1];
+    // 情况三
+    if (rightBorder - leftBorder > 1) return [leftBorder + 1, rightBorder - 1];
+    // 情况二
+    return [-1, -1];
+};
 ```
 
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