Added practice problems and solutions for binary search

Author: joncalhoun

002_binary_search/practice_problems/001_strings/main.go

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+package main
+
+import "fmt"
+
+// Given a list of sorted words (strings with no spaces),
+// search for a user provided word in the list without
+// being case sensitive. Return -1 if the word isn't found
+// and return the index of the word if it is found.
+func main() {
+	var words []string = []string{
+		"ALLigator",
+		"bat",
+		"bEEtle",
+		"camel",
+		"cat",
+		"cheetah",
+		"COLT",
+		"cow",
+		"dog",
+		"eagle",
+		"froG",
+		"hamster",
+		"horse",
+		"mink",
+		"moose",
+		"porcupine",
+		"RaT",
+		"rooster",
+		"steer",
+	}
+	fmt.Println("Sorted Words:", words)
+	var toFind string
+	fmt.Println("What word should we search for? No spaces please!")
+	fmt.Scanf("%s", &toFind)
+	var index int
+	index = binSearch(words, toFind)
+	if index < 0 {
+		fmt.Println("The word", toFind, "could not be found!")
+	} else {
+		fmt.Println("The word", toFind, "was found at index:", index, words[index])
+	}
+}
+
+func binSearch(words []string, word string) int {
+	return -1
+}

002_binary_search/practice_problems/001_strings_solution/main.go

@@ -0,0 +1,81 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+)
+
+// Given a list of sorted words (strings with no spaces),
+// search for a user provided word in the list without
+// being case sensitive. Return -1 if the word isn't found
+// and return the index of the word if it is found.
+func main() {
+	var words []string = []string{
+		"ALLigator",
+		"bat",
+		"bEEtle",
+		"camel",
+		"cat",
+		"cheetah",
+		"COLT",
+		"cow",
+		"dog",
+		"eagle",
+		"froG",
+		"hamster",
+		"horse",
+		"mink",
+		"moose",
+		"porcupine",
+		"RaT",
+		"rooster",
+		"steer",
+	}
+	fmt.Println("Sorted Words:", words)
+	var toFind string
+	fmt.Println("What word should we search for? No spaces please!")
+	fmt.Scanf("%s", &toFind)
+	var index int
+	index = binSearch(words, toFind)
+	if index < 0 {
+		fmt.Println("The word", toFind, "could not be found!")
+	} else {
+		fmt.Println("The word", toFind, "was found at index:", index, words[index])
+	}
+}
+
+func binSearch(words []string, word string) int {
+	var lo int = 0
+	var hi int = len(words) - 1
+
+	for lo <= hi {
+		var mid int = lo + (hi-lo)/2
+		var midValue string = words[mid]
+
+		if compare(midValue, word) == 0 {
+			return mid
+		} else if compare(midValue, word) > 0 {
+			// We want to use the left half of our list
+			hi = mid - 1
+		} else {
+			// We want to use the right half of our list
+			lo = mid + 1
+		}
+	}
+
+	// If we get here we tried to look at an invalid sub-list
+	// which means the number isn't in our list.
+	return -1
+}
+
+func compare(a, b string) int {
+	var aLow string = strings.ToLower(a)
+	var bLow string = strings.ToLower(b)
+	if aLow == bLow {
+		return 0
+	} else if aLow < bLow {
+		return -1
+	} else {
+		return 1
+	}
+}

002_binary_search/practice_problems/002_square_root/main.go

@@ -0,0 +1,15 @@
+package main
+
+import "fmt"
+
+// Use a binary search to find the square root of a number
+func main() {
+	var number float64 = 128.0
+	fmt.Println("Number:", number)
+	var squareRoot float64 = squareRoot(number)
+	fmt.Println("Square root:", squareRoot)
+}
+
+func squareRoot(n float64) float64 {
+	return n
+}

002_binary_search/practice_problems/002_square_root_solution/main.go

@@ -0,0 +1,25 @@
+package main
+
+import "fmt"
+
+// Use a binary search to find the square root of a number
+func main() {
+	var number float64 = 128.0
+	fmt.Println("Number:", number)
+	var squareRoot float64 = squareRoot(number)
+	fmt.Println("Square root:", squareRoot)
+}
+
+func squareRoot(n float64) float64 {
+	lo := 0.0
+	hi := n
+	for i := 0; i < 2000; i++ {
+		mid := lo + (hi-lo)/2.0
+		if mid*mid > n {
+			hi = mid
+		} else {
+			lo = mid
+		}
+	}
+	return lo
+}