Binary Search 2

Problem1.java

@@ -0,0 +1,53 @@
+class Problem1 {
+    public int[] searchRange(int[] nums, int target) {
+
+
+        int first = binarySearchFirst(nums, target, 0, nums.length-1);
+
+        if(first == -1) return new int[]{-1,-1};
+
+        int last = binarySearchLast(nums, target, first, nums.length-1);
+
+        return new int[]{first, last};
+    }
+
+    private int binarySearchFirst(int[] nums, int target, int low, int high){
+
+        while(low <= high){
+            int mid = low + (high - low)/2;
+            if(nums[mid] == target){
+                if(mid == 0 || nums[mid-1] != target){
+                    return mid;
+                }else{
+                    high = mid - 1;
+                }
+            }else if(nums[mid] > target){
+                high = mid - 1;
+            }else{
+                low = mid + 1;
+            }
+        }
+
+        return -1;
+    }
+
+    private int binarySearchLast(int[] nums, int target, int low, int high){
+
+        while(low <= high){
+            int mid = low + (high - low)/2;
+            if(nums[mid] == target){
+                if(mid == nums.length-1 || nums[mid+1] != target){
+                    return mid;
+                }else{
+                    low = mid + 1;
+                }
+            }else if(nums[mid] > target){
+                high = mid - 1;
+            }else{
+                low = mid + 1;
+            }
+        }
+
+        return -1;
+    }
+}

Problem2.java

@@ -0,0 +1,24 @@
+class Problem2 {
+    public int findMin(int[] nums) {
+        int n = nums.length;
+        int low = 0, 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; // fallback (should not reach)
+    }
+}

Problem3.java

@@ -0,0 +1,21 @@
+class Problem3 {
+    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;
+    }
+}