From c98d66aca04d0d839833b6b81bf249822c4ca350 Mon Sep 17 00:00:00 2001
From: Iru Cai <mytbk920423@gmail.com>
Date: Sat, 26 May 2018 14:27:47 +0800
Subject: 53, 55, 56

---
 euler53.c     | 26 ++++++++++++++++++++++++++
 euler55.scala | 20 ++++++++++++++++++++
 euler56.scala | 24 ++++++++++++++++++++++++
 3 files changed, 70 insertions(+)
 create mode 100644 euler53.c
 create mode 100644 euler55.scala
 create mode 100644 euler56.scala

diff --git a/euler53.c b/euler53.c
new file mode 100644
index 0000000..3e71c87
--- /dev/null
+++ b/euler53.c
@@ -0,0 +1,26 @@
+#include <stdio.h>
+
+/* number of r s.t. C(n, r)>x */
+int nr_ncr_bigger(int n, int x)
+{
+	int prod = 1;
+	int r = 0;
+
+	while (prod <= x && r*2 < n) {
+		r++;
+		prod = prod * (n-r+1) / r;
+	}
+
+	if (prod <= x)
+		return 0;
+	else
+		return n - r*2 + 1;
+}
+
+int main()
+{
+	int cnt = 0;
+	for (int i = 1; i <= 100; i++)
+		cnt += nr_ncr_bigger(i, 1000000);
+	printf("%d\n", cnt);
+}
diff --git a/euler55.scala b/euler55.scala
new file mode 100644
index 0000000..a36b6cd
--- /dev/null
+++ b/euler55.scala
@@ -0,0 +1,20 @@
+object Lychrel
+{
+  def lychrel(a: Int): Boolean = {
+    var t: BigInt = a
+    for (i <- 1 until 50) {
+      t = t + BigInt(t.toString.reverse)
+      if (t.toString == t.toString.reverse)
+        return false
+    }
+    true
+  }
+
+  def main(args: Array[String]) = {
+    var cnt = 0
+    for (i <- 1 until 10000)
+      if (lychrel(i)) cnt = cnt + 1
+
+    println(cnt)
+  }
+}
diff --git a/euler56.scala b/euler56.scala
new file mode 100644
index 0000000..a302b25
--- /dev/null
+++ b/euler56.scala
@@ -0,0 +1,24 @@
+object Lychrel
+{
+  def digital_sum(a: BigInt): Int = {
+    var sum: Int = 0
+    var t = a
+    while (t > 0) {
+      sum = sum + (t % 10).toInt
+      t = t / 10
+    }
+    sum
+  }
+
+  def main(args: Array[String]) = {
+    var maxsum = 0
+    for (a <- 2 until 100) {
+      var t: BigInt = 1
+      for (b <- 1 until 100) {
+        t = t * a
+        maxsum = maxsum max digital_sum(t)
+      }
+    }
+    println(maxsum)
+  }
+}
-- 
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