二分查找的变体 by golang

go/15_binarysearch/binarysearch.go

@@ -45,3 +45,111 @@ func bs(a []int, v int, low, high int) int {
 		return bs(a, v, mid+1, high)
 	}
 }
+
+//查找第一个等于给定值的元素
+func BinarySearchFirst(a []int, v int) int {
+	n := len(a)
+	if n == 0 {
+		return -1
+	}
+
+	low := 0
+	high := n - 1
+	for low <= high {
+		mid := (low + high) >> 1
+		if a[mid] > v {
+			high = mid - 1
+		} else if a[mid] < v {
+			low = mid + 1
+		} else {
+			if mid == 0 || a[mid-1] != v {
+				return mid
+			} else {
+				high = mid - 1
+			}
+		}
+	}
+
+	return -1
+}
+
+//查找最后一个值等于给定值的元素
+func BinarySearchLast(a []int, v int) int {
+	n := len(a)
+	if n == 0 {
+		return -1
+	}
+
+	low := 0
+	high := n - 1
+	for low <= high {
+		mid := (low + high) >> 1
+		if a[mid] > v {
+			high = mid - 1
+		} else if a[mid] < v {
+			low = mid + 1
+		} else {
+			if mid == n-1 || a[mid+1] != v {
+				return mid
+			} else {
+				low = mid + 1
+			}
+		}
+	}
+
+	return -1
+}
+
+//查找第一个大于等于给定值的元素
+func BinarySearchFirstGT(a []int, v int) int {
+	n := len(a)
+	if n == 0 {
+		return -1
+	}
+
+	low := 0
+	high := n - 1
+	for low <= high {
+		mid := (high + low) >> 1
+		if a[mid] > v {
+			high = mid - 1
+		} else if a[mid] < v {
+			low = mid + 1
+		} else {
+			if mid != n-1 && a[mid+1] > v {
+				return mid + 1
+			} else {
+				low = mid + 1
+			}
+		}
+	}
+
+	return -1
+}
+
+//查找最后一个小于等于给定值的元素
+func BinarySearchLastLT(a []int, v int) int {
+	n := len(a)
+	if n == 0 {
+		return -1
+	}
+
+	low := 0
+	high := n - 1
+	for low <= high {
+		mid := (low + high) >> 1
+		if a[mid] > v {
+			high = mid - 1
+		} else if a[mid] < v {
+			low = mid + 1
+		} else {
+			if mid == 0 || a[mid-1] < v {
+				return mid - 1
+			} else {
+				high = mid - 1
+			}
+		}
+	}
+
+	return -1
+}

go/15_binarysearch/binarysearch_test.go

@@ -25,3 +25,79 @@ func TestBinarySearchRecursive(t *testing.T) {
 		t.Fatal(BinarySearch(a, 4))
 	}
 }
+
+func TestBinarySearchFirst(t *testing.T) {
+	var a []int
+
+	a = []int{1, 2, 2, 2, 3, 4}
+	if BinarySearchFirst(a, 2) != 1 {
+		t.Fatal(BinarySearchFirst(a, 2))
+	}
+
+	a = []int{1, 2, 2, 2, 3, 4}
+	if BinarySearchFirst(a, 3) != 4 {
+		t.Fatal(BinarySearchFirst(a, 3))
+	}
+}
+
+func TestBinarySearchLast(t *testing.T) {
+	var a []int
+
+	a = []int{1, 2, 2, 2, 3, 4}
+	if BinarySearchLast(a, 2) != 3 {
+		t.Fatal(BinarySearchLast(a, 2))
+	}
+
+	a = []int{1, 2, 2, 2, 3, 4}
+	if BinarySearchLast(a, 3) != 4 {
+		t.Fatal(BinarySearchLast(a, 3))
+	}
+}
+
+func TestBinarySearchFirstGT(t *testing.T) {
+	var a []int
+
+	a = []int{1, 2, 2, 2, 3, 4}
+	if BinarySearchFirstGT(a, 2) != 4 {
+		t.Fatal(BinarySearchFirstGT(a, 2))
+	}
+
+	a = []int{1, 2, 2, 2, 3, 4}
+	if BinarySearchFirstGT(a, 1) != 1 {
+		t.Fatal(BinarySearchFirstGT(a, 1))
+	}
+
+	a = []int{1, 2, 2, 2, 3, 4}
+	if BinarySearchFirstGT(a, 3) != 5 {
+		t.Fatal(BinarySearchFirstGT(a, 3))
+	}
+
+	a = []int{1, 2, 2, 2, 3, 4}
+	if BinarySearchFirstGT(a, 4) != -1 {
+		t.Fatal(BinarySearchFirstGT(a, 4))
+	}
+}
+
+func TestBinarySearchLastLT(t *testing.T) {
+	var a []int
+
+	a = []int{1, 2, 2, 2, 3, 4}
+	if BinarySearchLastLT(a, 2) != 0 {
+		t.Fatal(BinarySearchLastLT(a, 2))
+	}
+
+	a = []int{1, 2, 2, 2, 3, 4}
+	if BinarySearchLastLT(a, 1) != -1 {
+		t.Fatal(BinarySearchLastLT(a, 1))
+	}
+
+	a = []int{1, 2, 2, 2, 3, 4}
+	if BinarySearchLastLT(a, 3) != 3 {
+		t.Fatal(BinarySearchLastLT(a, 3))
+	}
+
+	a = []int{1, 2, 2, 2, 3, 4}
+	if BinarySearchLastLT(a, 4) != 4 {
+		t.Fatal(BinarySearchLastLT(a, 4))
+	}
+}