179. Largest Number

README.md

@@ -23,6 +23,7 @@ continually updating 😃.
 * [121. Best Time to Buy and Sell Stock](src/0121_best_time_to_buy_and_sell_stock/maxprofit.go)   *`dynamic programming;`*  *`array`*
 * [122. Best Time to Buy and Sell Stock II](src/0122_best_time_to_buy_and_sell_stock_2/maxprofit.go)   *`greedy;`*  *`array`*
 * [167. Two Sum II - Input array is sorted](./src/0167_two_sum2/two_sum2.go)   *`double index;`*  *`binary search`*
+* [179. Largest Number](src/0179_largest_number/ln.go)   *`sort`*
 * [200. Number of Islands](src/0200_number_of_island/number_of_island.go)   *`dfs;`*  *`bfs`*
 * [209. Minimum Size Subarray Sum](./src/0209_minimum_size_subarray_sum/minimum_size_subarray_sum.go)   *`sliding window`*
 * [215. Kth Largest Element in an Array](./src/0215_kth_largest_element_in_an_array/kthleiaa.go)   *`sort`*

src/0179_largest_number/ln.go

@@ -0,0 +1,45 @@
+/*
+179. Largest Number
+https://leetcode.com/problems/largest-number/
+
+Given a list of non negative integers, arrange them such that they form the largest number.
+Note: The result may be very large, so you need to return a string instead of an integer.
+*/
+// time: 2019-01-14
+
+package ln
+
+import (
+	"sort"
+	"strconv"
+	"strings"
+)
+
+type sliceString []string
+
+// Len is the number of elements in the collection.
+func (s sliceString) Len() int { return len(s) }
+
+// Swap swaps the elements with indexes i and j.
+func (s sliceString) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
+
+// Less reports whether the element with
+// index i should sort before the element with index j.
+func (s sliceString) Less(i, j int) bool { return (s[i] + s[j]) > (s[j] + s[i]) }
+
+// time complexity: O(n log n), dominated by the complexity of sort.
+// space complexity: O(n)
+func largestNumber(nums []int) string {
+	numsString := make([]string, 0)
+	for _, num := range nums {
+		numsString = append(numsString, strconv.Itoa(num))
+	}
+
+	sort.Sort(sliceString(numsString))
+	numStr := strings.Join(numsString, "")
+
+	if strings.HasPrefix(numStr, "0") {
+		return "0"
+	}
+	return numStr
+}

src/0179_largest_number/ln_test.go

@@ -0,0 +1,23 @@
+package ln
+
+import "testing"
+
+func TestLargestNumber(t *testing.T) {
+	testCases := [][]int{
+		{10, 2},
+		{3, 30, 34, 5, 9},
+		{0},
+	}
+
+	expected := []string{
+		"210",
+		"9534330",
+		"0",
+	}
+
+	for index, nums := range testCases {
+		if res := largestNumber(nums); res != expected[index] {
+			t.Errorf("expected %s, got %s", expected[index], res)
+		}
+	}
+}

src/README.md

@@ -63,6 +63,7 @@
 |0155|[155. Min Stack](0155_min_stack/min_stack.go)|Easy|*`stack`*|
 |0165|[165. Compare Version Numbers](0165_compare_version_numbers/compare_version_numbers.go)|Medium|*`string`*|
 |0167|[Two Sum II - Input array is sorted](./0167_two_sum2/two_sum2.go)|Easy|*`对撞指针(双索引)`*|
+|0179|[179. Largest Number](0179_largest_number/ln.go)|Medium|*`sort`*|
 |0198|[House Robber](./0198_house_robber/house_robber.go)|Easy|*`memory search;`* *`dynamic programming`*|
 |0200|[200. Number of Islands](0200_number_of_island/number_of_island.go)|Medium|*`dfs;`* *`bfs`*|
 |0203|[203. Remove Linked List Elements](0203_remove_linked_list_elements/remove_linked_list_elements.go)|Easy|*`linked list`*|