From 9383aba292819d13a3140d5e277c548c3bd312b4 Mon Sep 17 00:00:00 2001
From: VicRen <vic.ren@me.com>
Date: Wed, 6 Jan 2021 08:47:13 +0800
Subject: [PATCH] update  euler 206

---
 206_concealed_square/main.go      | 21 ++++++++++--
 206_concealed_square/main_test.go | 55 +++++++++++++++++++++++++++++++
 2 files changed, 73 insertions(+), 3 deletions(-)

diff --git a/206_concealed_square/main.go b/206_concealed_square/main.go
index d1b3964..ab60eb8 100644
--- a/206_concealed_square/main.go
+++ b/206_concealed_square/main.go
@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"math"
 	"math/big"
+	"time"
 )
 
 func main() {
@@ -11,20 +12,34 @@ func main() {
 }
 
 func solution() {
+	ts := time.Now()
 	n := math.Sqrt(19293949596979899)
 	t := math.Sqrt(10203040506070809)
 	for i := n; i >= t; i-- {
-		if i == 1389019170 {
-			fmt.Println(i)
-		}
 		x := (&big.Int{}).SetInt64(int64(i))
+		if !isEndsWith37(x.String()) {
+			continue
+		}
 		if isMatch(x.Mul(x, x)) {
 			fmt.Println(x)
 			fmt.Println("num is", int64(i)*10)
+			fmt.Println(time.Since(ts))
+			break
 		}
 	}
 }
 
+func isEndsWith37(s string) bool {
+	if len(s) == 0 {
+		return false
+	}
+	c := s[len(s)-1]
+	if c == '3' || c == '7' {
+		return true
+	}
+	return false
+}
+
 func isMatch(i *big.Int) bool {
 	x := i.String()
 	num := x[0]
diff --git a/206_concealed_square/main_test.go b/206_concealed_square/main_test.go
index e314369..0357ac1 100644
--- a/206_concealed_square/main_test.go
+++ b/206_concealed_square/main_test.go
@@ -7,6 +7,7 @@ import (
 
 func Test_isMatch(t *testing.T) {
 	fn, _ := (&big.Int{}).SetString("10203040506070809", 0)
+	fn2, _ := (&big.Int{}).SetString("10203040506070808", 0)
 	type args struct {
 		i *big.Int
 	}
@@ -22,6 +23,13 @@ func Test_isMatch(t *testing.T) {
 			},
 			true,
 		},
+		{
+			"test2",
+			args{
+				fn2,
+			},
+			false,
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -31,3 +39,50 @@ func Test_isMatch(t *testing.T) {
 		})
 	}
 }
+
+func Test_isEndsWith37(t *testing.T) {
+	type args struct {
+		s string
+	}
+	tests := []struct {
+		name string
+		args args
+		want bool
+	}{
+		{
+			"test1",
+			args{
+				"123",
+			},
+			true,
+		},
+		{
+			"test2",
+			args{
+				"127",
+			},
+			true,
+		},
+		{
+			"test3",
+			args{
+				"12",
+			},
+			false,
+		},
+		{
+			"test4",
+			args{
+				"",
+			},
+			false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := isEndsWith37(tt.args.s); got != tt.want {
+				t.Errorf("isEndsWith37() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}