add new files

Author: anakin

17. Letter Combinations of a Phone Number.go

@@ -0,0 +1,21 @@
+package main
+
+func letterCombinations(digits string) []string {
+	table := []string{"", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"}
+	ret := []string{}
+	if len(digits) > 0 {
+		help(&ret, digits, "", 0, table)
+	}
+	return ret
+}
+
+func help(ret *[]string, digits string, cur string, index int, table []string) {
+	if index == len(digits) {
+		*ret = append(*ret, cur)
+		return
+	}
+	tmp := table[digits[index]-48]
+	for _, t := range tmp {
+		help(ret, digits, cur+string(t), index+1, table)
+	}
+}

46. Permutations.go

@@ -0,0 +1,26 @@
+package main
+
+func permute(nums []int) [][]int {
+	var ret [][]int
+	l := len(nums)
+	if l == 0 {
+		return ret
+	}
+	helper(nums, 0, l-1, &ret)
+	return ret
+}
+
+func helper(nums []int, begin, end int, ret *[][]int) {
+	if begin == end {
+		t := make([]int, len(nums))
+		copy(t, nums) //这里一定要copy
+		*ret = append(*ret, t)
+		return
+	}
+
+	for i := begin; i <= end; i++ {
+		nums[begin], nums[i] = nums[i], nums[begin]
+		helper(nums, begin+1, end, ret)
+		nums[begin], nums[i] = nums[i], nums[begin]
+	}
+}

463. Island Perimeter.go

@@ -0,0 +1,28 @@
+package main
+
+func islandPerimeter(grid [][]int) int {
+	row := len(grid)
+	col := len(grid[0])
+	count := 0
+	for i := 0; i < row; i++ {
+		for j := 0; j < col; j++ {
+			if grid[i][j] == 1 {
+				t := 4
+				if j >= 1 && grid[i][j-1] == 1 { //左边有邻居
+					t--
+				}
+				if j < col-1 && grid[i][j+1] == 1 { //右边有邻居
+					t--
+				}
+				if i >= 1 && grid[i-1][j] == 1 { //上面有邻居
+					t--
+				}
+				if i < row-1 && grid[i+1][j] == 1 { //下面有邻居
+					t--
+				}
+				count += t
+			}
+		}
+	}
+	return count
+}

75. Sort Colors.go

@@ -0,0 +1,25 @@
+package main
+
+func swap(nums []int, i, j int) {
+	tmp := nums[i]
+	nums[i] = nums[j]
+	nums[j] = tmp
+}
+func sortColors(nums []int) {
+	l, i, r := 0, 0, len(nums)-1
+	for i <= r {
+		if nums[i] == 0 {
+			swap(nums, i, l)
+			i++
+			l++
+		} else {
+			if nums[i] == 1 {
+				i++
+			} else {
+				swap(nums, i, r)
+				r--
+			}
+
+		}
+	}
+}

8. String to Integer (atoi).go

@@ -0,0 +1,42 @@
+package main
+
+import (
+	"math"
+	"strings"
+)
+
+func myAtoi(str string) int {
+	pos := 1
+	res := 0
+	str = strings.TrimSpace(str)
+	if len(str) == 0 {
+		return res
+	}
+	i := 0
+	if str[i] == '+' {
+		i++
+		pos = 1
+	} else if str[i] == '-' {
+		i++
+		pos = -1
+	}
+	for ; i < len(str); i++ {
+		if pos*res >= math.MaxInt32 {
+			return math.MaxInt32
+		}
+		if pos*res <= math.MinInt32 {
+			return math.MinInt32
+		}
+		if str[i] < '0' || string(str[i]) > "9" {
+			return res * pos
+		}
+		res = res*10 + int(str[i]) - '0'
+	}
+	if pos*res >= math.MaxInt32 {
+		return math.MaxInt32
+	}
+	if pos*res <= math.MinInt32 {
+		return math.MinInt32
+	}
+	return pos * res
+}