确定循环中的迭代次数 (Java)

Question

我想知道是否有人知道有一个公式可以预先计算循环中的迭代次数。

我试了一下，得到了等式：

迭代次数等于（（终值与初值之差的绝对值）加上（increment/decrement的绝对值））除以增量的绝对值/ 递减

或

expected = (int)((Math.abs(final-initial) + Math.abs(iteration)) / iteration),

例如：

for(int i = 43; i > 9; i-=8) ，将运行 5 次，因为 43-10 （如果不包括，则在初始值上加一个） = 33+8 = 41/8 ~ 5

如果它等于或大于- for(int i = 43; I >= 9; i-=8), 那么你会根据 (43-9+8) / 8 (5)我的公式

我已经测试了几次，但还不确定。

谢谢。

Answer 1

排除循环的任何特殊中断（中断、改变计数器等），您可以测试下面的公式。如果终止测试是 < 而不是 <= 你应该从开始减去 1。

total iterations = (end - start + incr)/incr; // for <=
total iterations = (end - start  + incr - 1)/incr; // for <

Random r = new Random();
for (int k = 0; k < 10000; k++) {
    int count = 0;
    int start = r.nextInt(20)+1;
    int end = r.nextInt(1000) + start+1;
    int incr = r.nextInt(50)+1;
    
    for (int i = start; i <= end; i += incr) {
        count++;
    }
    
    int calc = (end - start + incr - 1)/incr;
    if (calc != count) {
        System.out.println("Oops");
    }
}

Answer 2

排除循环的任何特殊中断（中断、改变计数器等），公式如下：

iterations = (end - start+incr)/incr，其中关系运算符为 >= 或 <=

如果关系运算符是 < 或 >，则迭代次数 = (end - start+incr-1)/incr

这个可以测试如下

/*
 * Baring any special disruption of the loop (breaks, altering counter, etc), the formula is as follows:

iterations = (|start-end|+|incr|)/|incr|, where relational operator is >= or <=

- if relational operator is < or >, then iterations = ((|start-end|+|incr|-1)/|incr|

 * @author rahul.arora, WJS
 */

import java.util.Random;

public class LoopIterationCalcTester {

    public static void main(String[] args) {
        
        
    for (int x = 0; x < 100; x++) {
        Random r = new Random();
        for (int k = 0; k < 10000; k++) {
            int count = 0;
            int start = r.nextInt(20)+1;
            int end = r.nextInt(1000) + 20;
            int incr = r.nextInt(50)+1;
            
            for (int i = start; i < end; i += incr) {
                count++;
            }
            
            int calc = (end - start-1+incr)/incr;
            
            if (calc != count) {
                System.out.println("Oops");
               
            }
        }
        
        
        for (int k = 0; k < 10000; k++) {
            int count = 0;
            int start = r.nextInt(20)+1;
            int end = r.nextInt(1000) + 20;
            int incr = r.nextInt(50)+1;
            
            for (int i = start; i <= end; i += incr) {
                count++;
            }
            
            int calc = (end - start+incr)/incr;
            
            if (calc != count) {
                System.out.println("Oops");
             
            }
        }
        for (int k = 0; k < 10000; k++) {
            int count = 0;
            int start = r.nextInt(20)+1;
            int end = r.nextInt(1000) + 20;
            int incr = r.nextInt(50)+1;
            
            for (int i = end; i >= start; i -= incr) {
                count++;
            }
            
            int calc = (end - start+incr)/incr;
            
            if (calc != count) {
                System.out.println("Oops");
            
            }
        }
        for (int k = 0; k < 10000; k++) {
            int count = 0;
            int start = r.nextInt(20)+1;
            int end = r.nextInt(1000) + 20;
            int incr = r.nextInt(50)+1;
            
            for (int i = end; i > start; i -= incr) {
                count++;
            }
            
            int calc = (end - start-1+incr)/incr;
            
            if (calc != count) {
                System.out.println("Oops");
            
            }
        }
        }
    }

}

确定循环中的迭代次数 (Java)

Determining Number of Iterations in a loop (Java)

java

algorithm

formula