Add Solution CPP[34]

solution/0034.Find First and Last Position of Element in Sorted Array/README.md

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+## 在排序数组中查找元素的第一个和最后一个位置
+
+### 问题描述
+
+给定一个按照升序排列的整数数组 nums，和一个目标值 target。找出给定目标值在数组中的开始位置和结束位置。
+
+你的算法时间复杂度必须是 O(log n) 级别。
+
+如果数组中不存在目标值，返回 [-1, -1]。
+
+```
+示例 1:
+输入: nums = [5,7,7,8,8,10], target = 8
+输出: [3,4]
+
+示例 2:
+输入: nums = [5,7,7,8,8,10], target = 6
+输出: [-1,-1]
+```
+
+### 思路
+
+二分查找找下标，找到下标对其左右查找是否等于目标值就好了
+
+```CPP
+
+class Solution {
+public:
+    bool binarySearch(vector<int> &nums,int &target,int &pos,int left,int right){
+        int mid = left + ((right - left) >> 1);
+        if(nums[left] == target){
+            pos = left;
+            return true;
+        }
+        if(nums[right] == target){
+            pos = right;
+            return true;
+        }
+        if(nums[mid] == target){
+            pos = mid;
+            return true;
+        }
+
+        if(left == mid){
+            return false;
+        }
+        else if(nums[mid] > target){
+            return binarySearch(nums,target,pos,left,mid-1);
+        }
+        else if(nums[mid] < target){
+            return binarySearch(nums,target,pos,mid+1,right);
+        } 
+
+        return false;
+    }
+
+    vector<int> searchRange(vector<int>& nums, int target) {
+        int pos = 0;
+        int len = nums.size();
+        if(len == 0)return {-1,-1};
+        if(binarySearch(nums,target,pos,0,len-1)){
+            int left = pos;
+            int right = pos;
+            while(left>0 && nums[left-1] == nums[pos])left--;
+            while(right<len-1 && nums[right+1] == nums[pos])right++;
+            return {left,right};
+        }
+        else{
+            return {-1,-1};
+        }
+    }
+};
+```

solution/0034.Find First and Last Position of Element in Sorted Array/Solution.cpp

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+class Solution {
+public:
+    bool binarySearch(vector<int> &nums,int &target,int &pos,int left,int right){
+        int mid = left + ((right - left) >> 1);
+        if(nums[left] == target){
+            pos = left;
+            return true;
+        }
+        if(nums[right] == target){
+            pos = right;
+            return true;
+        }
+        if(nums[mid] == target){
+            pos = mid;
+            return true;
+        }
+
+        if(left == mid){
+            return false;
+        }
+        else if(nums[mid] > target){
+            return binarySearch(nums,target,pos,left,mid-1);
+        }
+        else if(nums[mid] < target){
+            return binarySearch(nums,target,pos,mid+1,right);
+        } 
+
+        return false;
+    }
+
+    vector<int> searchRange(vector<int>& nums, int target) {
+        int pos = 0;
+        int len = nums.size();
+        if(len == 0)return {-1,-1};
+        if(binarySearch(nums,target,pos,0,len-1)){
+            int left = pos;
+            int right = pos;
+            while(left>0 && nums[left-1] == nums[pos])left--;
+            while(right<len-1 && nums[right+1] == nums[pos])right++;
+            return {left,right};
+        }
+        else{
+            return {-1,-1};
+        }
+    }
+};