[Leetcode 34] Youngsang Solution

Leetcode/34/ysuh/README.md

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+## Link
+[Find First and Last Position of Element in Sorted Array](https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array/description/) 
+
+## Topic
+binary search 
+
+## Approach
+find the target via binary search
+find the left and right via binary recursive search 
+
+## Note

Leetcode/34/ysuh/solution.cpp

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+class Solution {
+public:
+    vector<int> binarySearch(vector<int>& nums, int target, int start, int end) {
+        while (start <= end) {
+            int mid = (start + end) / 2;
+            if (nums[mid] == target) {
+                return {findLeft(nums, target, start, mid-1), findRight(nums, target, mid+1, end)};
+            } else if (nums[mid] > target) {
+                end = mid - 1;
+            } else {
+                start = mid + 1;
+            }
+        }
+        return {-1, -1};
+    }
+
+    int findLeft(vector<int>& nums, int target, int start, int end) {
+        while (start <= end) {
+            int mid = (start + end) / 2;
+            if (nums[mid] == target) {
+                return findLeft(nums, target, start, mid-1);
+            } else if (nums[mid] > target) {
+                end = mid - 1;
+            } else {
+                start = mid + 1;
+            }
+        }
+        return end + 1;
+    }
+
+    int findRight(vector<int>& nums, int target, int start, int end) {
+        while (start <= end) {
+            int mid = (start + end) / 2;
+            if (nums[mid] == target) {
+                return findRight(nums, target, mid+1, end);
+            } else if (nums[mid] > target) {
+                end = mid - 1;
+            } else {
+                start = mid + 1;
+            }
+        }
+        return start - 1;
+    }
+
+    vector<int> searchRange(vector<int>& nums, int target) {
+        if (!nums.size()) return {-1, -1};
+        return binarySearch(nums, target, 0, nums.size()-1);
+    }
+};