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Commit e4604b7

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binary search (leftmost element) implementation and tests, leetcode Find Target Indices After Sorting Array problem solution
1 parent bf829c5 commit e4604b7

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4 files changed

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4 files changed

+163
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package binary_search
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func BinarySearchLeftmost(a []int, target int) (int, bool) {
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l, r := 0, len(a)
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for l < r {
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m := (l + r) / 2 // similar to floor((l+r)/2) https://go.dev/ref/spec#Arithmetic_operators, see Integer operators
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if a[m] < target {
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l = m + 1
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} else {
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r = m
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}
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}
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return l, l < len(a) && a[l] == target
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}
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package binary_search
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import "testing"
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func TestBinarySearchLeftmost(t *testing.T) {
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cases := []testCase{
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// 0. Regular case
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{
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arr: []int{3, 4, 5, 6, 7, 7, 8, 9},
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target: 7,
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expIdx: 4,
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expFound: true,
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},
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// 1. Empty array
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{
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arr: []int{},
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target: 7,
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expIdx: 0,
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expFound: false,
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},
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// 2. Single element array doesn't contains element
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{
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arr: []int{1},
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target: 7,
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expIdx: 0,
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expFound: false,
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},
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// 3. Single element array contains element
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{
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arr: []int{7},
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target: 7,
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expIdx: 0,
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expFound: true,
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},
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// 4. No value (in the middle)
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{
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arr: []int{-1, -2, 2, 4, 6, 7, 9},
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target: 5,
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expIdx: 0,
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expFound: false,
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},
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// 5. No value (less than min value in the array)
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{
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arr: []int{-10, -2, -1, 4, 6, 7, 9},
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target: -30,
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expIdx: 0,
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expFound: false,
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},
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// 6. No value (more than max value in the array)
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{
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arr: []int{-10, -2, -1, 4, 6, 7, 9},
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target: 50,
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expIdx: 0,
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expFound: false,
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},
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// 7. First element
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{
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arr: []int{-10, -2, -1, 4, 6, 7, 9},
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target: -10,
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expIdx: 0,
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expFound: true,
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},
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// 8. Last element
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{
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arr: []int{-12, -10, -2, -1, 4, 6, 7, 9},
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target: 9,
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expIdx: 7,
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expFound: true,
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},
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}
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for caseNum, tc := range cases {
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idx, found := BinarySearchLeftmost(tc.arr, tc.target)
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if found != tc.expFound {
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t.Errorf("case %d error: expecting found=%v, got: %v\n", caseNum, tc.expFound, found)
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}
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if !tc.expFound { // idx can be random in such case
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continue
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}
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if idx != tc.expIdx {
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t.Errorf("case %d error: expecting idx=%d, got %d\n", caseNum, tc.expIdx, idx)
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}
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}
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}
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// https://leetcode.com/problems/find-target-indices-after-sorting-array/
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package find_target_indices_after_sorting_array
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import (
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"sort"
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)
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func targetIndices(nums []int, target int) []int {
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sort.Sort(sort.IntSlice(nums))
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// Find elements
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l, r := 0, len(nums)
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for l < r {
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m := (l + r) / 2
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if nums[m] < target {
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l = m + 1
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} else {
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r = m
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}
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}
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// Collect all indices
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res := make([]int, 0)
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for ; l < len(nums) && nums[l] == target; l++ {
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res = append(res, l)
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}
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return res
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}
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package find_target_indices_after_sorting_array
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import (
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"reflect"
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"testing"
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)
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func Test_targetIndices(t *testing.T) {
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cases := []struct {
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nums []int
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target int
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exp []int
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}{
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{
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nums: []int{1, 2, 5, 2, 3},
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target: 2,
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exp: []int{1, 2},
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},
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{
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nums: []int{1, 2, 5, 2, 3},
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target: 3,
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exp: []int{3},
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},
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{
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nums: []int{1, 2, 5, 2, 3},
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target: 5,
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exp: []int{4},
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},
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}
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for idx, tc := range cases {
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out := targetIndices(tc.nums, tc.target)
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if !reflect.DeepEqual(out, tc.exp) {
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t.Errorf("case %d error: \n-- got: %v\n-- expected: %v", idx, out, tc.exp)
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}
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}
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}

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