有人可以解释这两个循环之间的区别吗？

Question

   while(n>= 0 && nums[n] == value){  
        n--;
    }

   while(n>=0 && nums[n--] == value){
   }

我认为这两个循环应该完全相同.发生的是我运​​行测试用例输入[4,5]值= 4.并获得一个超出边界的数组索引.但是,如果我可以进入另一个循环,它就可以了.

public int removeElement(int[] nums, int val) {
    if(nums.length == 0) return 0;
    // use two pointers, n for the right most of the item, which value != val. 
    // i for the start pointer. 
    int n = nums.length-1;
    int i = 0;
    while(n>= 0 && nums[n--] == val){ 
    }

    while(i <= n){
        // as long as the curr items is equal to the valu
        // replace it by the right most of the value, decrement the n
        // pointer, until find another item which is not equal to val. 
        if(nums[i] == val){
            nums[i] = nums[n]; //
            while(n >= 0 && nums[--n] == val){
            }
        }
        i++;   
    }
    return n+1;
}

Answer 1

他们不一样.

在第一个循环中,n仅在n >= 0和时减少nums[n] = value.

public void loop1() {
    int n = 0;
    int[] nums = new int[]{1};
    int value = 2;

    // n >= 0 is true
    // nums[n] == value is false
    // Therefore while condition is false and n is NOT decremented
    while(n>= 0 && nums[n] == value){  
        n--;
    }
    // n = 0
    System.out.println("n=" + n);
}

在第二个循环中,无论是真还是假,n都会减少.n >= 0nums[n] == value

public void loop2() {
    int n = 0;
    int[] nums = new int[]{1};
    int value = 2;

    // n >= 0 is true
    // nums[n--] == value executes in 2 steps:
    //  1.  nums[n] == value
    //  2.  n = n - 1 WILL EXECUTE regardless of result being true/false
    while(n>= 0 && nums[n--] == value){  
    }
    // n = -1
    System.out.println("n=" + n);
}