Java recursion, tail recursion, non-recursion, and stack processing triangle number

Java recursion, tail recursion, non-recursion, and stack processing triangle number

 

 

Import java. io. bufferedReader; import java. io. inputStreamReader; // 1, 3, 6, 10, 15... n triangle number/** #1 * ## 1 + 2 * ### 1 + 2 + 3 * #### 1 + 2 + 3 + 4 *#### #1 + 2 + 3 + 4 + 5 *... the first layer is 1, and the nth layer is equal to n + (f (n-1) */public class TriangleNumber {static int triangle (int n) {if (n <1) return 0; if (n = 1) return 1; return n + triangle (n-1); // recursion to layer-4 calculation, returns the result recursively from the bottom layer and calculates the result with n and} // If a recursive call of a function appears at the end of the function, it is called the static int triangle (int n, int last) {// The last is initially passed 0 tail recursion if (n <1) return 0; if (n = 1) return 1 + last; return triangle (n-1, n + last); // recursively calculates the final result and returns the result at the bottom layer.} // non-recursive static int triangle2 (int n) {int sum = 0; for (int I = 1; I <= n; I ++) {sum + = I;} return sum;} static int str2Int (String num) {return Integer. valueOf (num);} // Save the stack. here is the value of each step in the computing process: private static class MyStack {int maxSize; int [] stackAry; int top; // index on the top of the stack MyStack (int max) {This. maxSize = max; this. stackAry = new int [maxSize]; top =-1;} void push (int n) {stackAry [++ top] = n;} int pop () {return stackAry [top --];} int peek () {return stackAry [top];} boolean isEmpty () {return top =-1 ;}} // implement static int triangle3 (int n) {MyStack stack = new MyStack (n); int result = 0; while (n> 0) {stack. push (n); n --;} while (! Stack. isEmpty () {int temp = stack. pop (); result + = temp;} return result;} public static void main (String [] args) throws Exception {System. out. println (----- program start. to calculate the maximum number of triangles, enter the number of digits (enter exit program) -----); BufferedReader br = new BufferedReader (new InputStreamReader (System. in); String line = br. readLine (); while (! Line. equals (exit) {int n = str2Int (line); System. out. println (recursion: + triangle (n); System. out. println (tail recursion: + triangle (n, 0); System. out. println (non-recursive: + triangle2 (n); System. out. println (stack implementation: + triangle3 (n); System. out. println (); System. out. println (----- program start. to calculate the maximum number of triangles, enter the number of digits (enter exit program) -----); line = br. readLine ();} System. out. println (----- program exit -----); Runtime. getRuntime (). exit (0 );}}

Test

 

 

----- The program starts. to calculate the number of triangle values, enter the number of digits (enter the exit program) ----- 10 recursion: 55 tail recursion: 55 non recursion: 55 stack implementation: 55 ----- the program starts. to calculate the maximum number of triangle values, enter the number of digits (enter the exit program) ----- 100 recursion: 5050 tail recursion: 5050 non recursion: 5050 stack implementation: 5050 ----- program start. to calculate the maximum number of triangles, enter the number of digits (enter exit program) ----- exit ----- program exit -----