dfs

leet_code/494.目标和/main.go

@@ -0,0 +1,50 @@
+package main
+
+import "fmt"
+
+func findTargetSumWays(nums []int, target int) int {
+	res := 0
+
+	//dfs(curSum, target, index, &res, nums, '+')
+	//dfs(curSum, target, index, &res, nums, '-')
+
+	dfsBetter(nums, target, 0, 0, &res)
+
+	return res
+}
+
+func dfsBetter(nums []int, target, sum, index int, res *int) {
+	if index == len(nums) {
+		if sum == target {
+			*res++
+		}
+	} else {
+		dfsBetter(nums, target, sum + nums[index], index + 1, res)
+		dfsBetter(nums, target, sum - nums[index], index + 1, res)
+	}
+}
+
+func dfs(curSum, target, index int, res *int, nums []int, op byte) {
+	if op == '+' {
+		curSum += nums[index]
+	} else {
+		curSum -= nums[index]
+	}
+	index++
+
+	if curSum == target && index == len(nums){
+		*res += 1
+		return
+	} else if index == len(nums) {
+		return
+	} else  {
+		dfs(curSum, target, index, res, nums, '+')
+		dfs(curSum, target, index, res, nums, '-')
+	}
+}
+
+
+
+func main() {
+	fmt.Println(findTargetSumWays([]int{1, 1, 1, 1, 1}, 3))
+}

main.go

@@ -2,28 +2,36 @@ package main
 
 import (
 	"fmt"
-	"reflect"
+	"os"
+	"time"
 )
 
 func main() {
-	chan1 := make(chan int, 1)
-	chan2 := make(chan string, 2)
-	chan3 := make(chan float64, 1)
+	defer fmt.Println("defer main")
+	var user = os.Getenv("USER_")
 
-	// 异步监听
 	go func() {
-		for {
-			// select 会等待某个管道就绪，若同时多个就绪，会随机选一个处理
-			select {
-			case params := <- chan1:
-				fmt.Println(params)
-			case <- chan2:
-			case <- chan3:
-			default:
-				// do nothing
+		defer func() {
+			fmt.Println("defer caller")
+			if err := recover(); err != nil {
+				fmt.Println("recover success. err: ", err)
 			}
-		}
+		}()
+
+		func() {
+			defer func() {
+				fmt.Println("defer here")
+			}()
+
+			if user == "" {
+				panic("should set user env.")
+			}
+
+			// 此处不会执行
+			fmt.Println("after panic")
+		}()
 	}()
 
-	reflect.SliceHeader{}
+	time.Sleep(100)
+	fmt.Println("end of main function")
 }