add: original solution for challenge3 similar problems

Pattern11 - Modified Binary Search/Challenge3-Rotation_Count/solution.go

@@ -1,5 +1,6 @@
 package challenge3rotationcount
 
+
 /*
 Given an array of numbers which is sorted in ascending order and is rotated ‘k’ times around a pivot, find ‘k’.
 
@@ -45,3 +46,42 @@ func countRotations(arr []int) int {
 
 	return 0
 }
+
+//
+// How do we find the rotation count of a sorted and rotated array that has duplicates too?
+// ref: https://leetcode-cn.com/problems/find-minimum-in-rotated-sorted-array-ii/
+//
+func countRotations2(arr []int) int {
+	var (
+		start = 0
+		end   = len(arr) - 1
+	)
+
+	for start < end {
+		mid := start + (end-start)/2
+		if mid < end && arr[mid] > arr[mid+1] {
+			return mid + 1
+		}
+		if mid > start && arr[mid-1] > arr[mid] {
+			return mid
+		}
+
+		if arr[start] == arr[mid] && arr[mid] == arr[end] {
+			// 这种情况需要判断start，end是否是最小值
+			if arr[start] > arr[start+1] {
+				return start + 1
+			}
+			start++
+			if arr[end-1] > arr[end] {
+				return end
+			}
+			end--
+		} else if arr[start] < arr[mid] || (arr[start] == arr[mid] && arr[mid] > arr[end]) {
+			start = mid + 1
+		} else {
+			end = mid - 1
+		}
+	}
+
+	return 0
+}

Pattern11 - Modified Binary Search/Challenge3-Rotation_Count/solution_test.go

@@ -1,6 +1,8 @@
 package challenge3rotationcount
 
-import "testing"
+import (
+	"testing"
+)
 
 func Test_countRotations(t *testing.T) {
 	type args struct {
@@ -24,3 +26,29 @@ func Test_countRotations(t *testing.T) {
 		})
 	}
 }
+
+func Test_countRotations2(t *testing.T) {
+	type args struct {
+		arr []int
+	}
+	tests := []struct {
+		name string
+		args args
+		want int
+	}{
+		{"case1", args{[]int{10, 15, 1, 3, 8}}, 2},
+		{"case2", args{[]int{4, 5, 7, 9, 10, -1, 2}}, 5},
+		{"case3", args{[]int{1, 3, 8, 10}}, 0},
+		{"case4", args{[]int{10, 1, 3, 8, 9}}, 1},
+		{"case5", args{[]int{3, 3, 7, 3}}, 3},
+		{"case6", args{[]int{3, 3, 3, 3, 7}}, 0},
+		{"case7", args{[]int{10, 1, 10, 10, 10}}, 1},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := countRotations2(tt.args.arr); got != tt.want {
+				t.Errorf("countRotations2() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}