problem 30 of project euler

Author: henryscala

rs/p030_digit_fifth_power.rs

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+//problem 30 of project euler 
+//digit fifth power
+//n digit number has a lower limit, which is 10^(n-1) , because the first digit is greater than 1  <-----first item 
+//the sum of fifth power of the digits has a upper limit, which is n*10^5<10^6      <------second item 
+//the first item grows fast than the second item. We only need to consider the numbers with at most 6 digits, 
+//otherwise, there is not overlap between the first item and the second item 
+
+
+fn nth_power_sum_of_digits(num:usize,n:usize)->usize {
+	let mut num :usize= num; 
+	let mut sum :usize= 0; 
+	while num > 0 {
+		let digit = num % 10;
+		if digit > 0 {
+			sum += digit.pow(n as u32); 
+		}
+		num = num / 10; 
+	}
+	sum 
+}
+
+fn main (){
+	let mut total = 0; 
+	let mut sum = 0; 
+	for i in 10..((10 as usize).pow(6 as u32)) {
+		let j = nth_power_sum_of_digits(i,5); 
+		if i==j {
+			println!("{}",i);
+			sum += i; 
+			total += 1; 
+		}
+	}
+
+	println!("total={}",total);
+	println!("sum={}",sum);
+}
+
+
+