Create: 0034-find-first-and-last-position-of-element-in-sorted-array.cpp

tonngw · tonngw · commit 2842da53c2da · 2023-05-31T22:21:53.000+08:00
diff --git a/cpp/0034-find-first-and-last-position-of-element-in-sorted-array.cpp b/cpp/0034-find-first-and-last-position-of-element-in-sorted-array.cpp
@@ -0,0 +1,32 @@
+/*
+    Given an array of integers nums sorted in non-decreasing order, find the starting and ending position of a given target value.
+    Ex. nums = [5,7,7,8,8,10], target = 8 -> [3, 4] (start position is 3, end position is 4)
+
+    Use binary search, firstly binary search left endpoint, then binary search right endpoint.
+
+    Time: O(log n)
+    Space: O(1)
+*/
+
+class Solution {
+public:
+    vector<int> searchRange(vector<int>& nums, int target) {
+        if (nums.empty()) return {-1, -1};
+        int l = 0, r = nums.size() - 1;
+        while (l < r) {
+            int mid = l + r >> 1;
+            if (nums[mid] >= target) r = mid;
+            else l = mid + 1;
+        }
+        if (nums[l] != target) return {-1, -1};
+        int left = l;
+
+        l = 0, r = nums.size() - 1;
+        while (l < r) {
+            int mid = l + r + 1ll >> 1;
+            if (nums[mid] <= target) l = mid;
+            else r = mid - 1;
+        }
+        return {left, r};
+    }
+};
