Solved Binarsearch 2 problems

find-first-and-last-pos.java

@@ -0,0 +1,53 @@
+//TC: O(logn)
+// SC: O(1)
+
+class Solution {
+    public int[] searchRange(int[] nums, int target) {
+        int n = nums.length;
+        if (nums == null || nums.length == 0 || target < nums[0] || target > nums[n - 1])
+            return new int[] { -1, -1 };
+
+        int first = binarySearchFirst(nums, 0, n - 1, target);
+        if (first == -1)
+            return new int[] { -1, -1 };
+        int second = binarySearchSecond(nums, first, n - 1, target);
+        return new int[] { first, second };
+    }
+
+    private int binarySearchFirst(int[] nums, int low, int high, int target) {
+        while (low <= high) {
+            int mid = low + (high - low) / 2;
+            if (nums[mid] == target) {
+                if (mid == 0 || nums[mid] > nums[mid - 1]) {
+                    return mid;
+                } else {
+                    high = mid - 1;
+                }
+            } else if (nums[mid] > target) {
+                high = mid - 1;
+            } else {
+                low = mid + 1;
+            }
+        }
+        return -1;
+    }
+
+    private int binarySearchSecond(int[] nums, int low, int high, int target) {
+        while (low <+ high) {
+            int mid = low + (high - low) / 2;
+            if (nums[mid] == target) {
+                if (mid == (nums.length - 1) || nums[mid] < nums[mid + 1]) {
+                    return mid;
+                } else {
+                    low = mid + 1;
+                }
+            } else if (nums[mid] > target) {
+                high = mid - 1;
+            } else {
+                low = mid + 1;
+            }
+        }
+        return low;
+    }
+
+}

find-min-rotated-sorted-array.java

@@ -0,0 +1,26 @@
+//TC: O(logn)
+//SC: O(1)
+
+
+class Solution {
+    public int findMin(int[] nums) {
+        int n = nums.length;
+        int low = 0;
+        int high = n - 1;
+
+        while (low <= high) {
+            if (nums[low] <= nums[high]) {
+                return nums[low];
+            }
+            int mid = low + (high - low) / 2;
+            if ((mid == 0 || nums[mid] <= nums[mid - 1]) && (mid == n - 1 || nums[mid] <= nums[mid + 1])) {
+                return nums[mid];
+            } else if (nums[low] <= nums[mid]){ //left sorted range
+                low = mid+1;
+            } else {
+                high = mid-1;
+            }
+        }
+        return -1;
+    }
+}

peak-element.java

@@ -0,0 +1,21 @@
+//TC: O(logn)
+//SC: O(1)
+
+class Solution {
+    public int findPeakElement(int[] nums) {
+        int n = nums.length;
+        int low = 0, high = n-1;
+
+        while (low <= high) {
+            int mid = low + (high - low) / 2;
+            if ((mid==0 || nums[mid] > nums[mid - 1]) && (mid == n-1 || nums[mid] > nums[mid + 1])) {
+                return mid;
+            } else if (nums[mid+1] > nums[mid]) {
+                low = mid + 1;
+            } else {
+                high = mid - 1;
+            }
+        }
+        return -1;
+    }
+}