Question

我们有一系列高度，代表沿着步道的高度。给定数组start / end索引，返回从start索引开始到end索引结束的步行的更改总和。例如，对于高度{5, 3, 6, 7, 2}和start=2，end=4会产生1 + 5 = 6的总和。起始端结束索引都是start <= end数组的有效索引。

sumHeights({5, 3, 6, 7, 2}, 2, 4) => 6       
sumHeights({5, 3, 6, 7, 2}, 0, 1) => 2       
sumHeights({5, 3, 6, 7, 2}, 0, 4) => 11

我正在努力做到这一点，我尝试了一部分，但我很困惑，我得到了ArrayIndexOutOfBoundsException。

 public int sumHeights(int[] heights, int start, int end) {        

   int total =0;   
   int difference =0;   
      for(int i=start;i<=end;i++){           
        if(heights[i] > heights[i++]){         
           difference =heights[i] - heights[i++];                  
        }else if(heights[i++] > heights[i]){         
           difference =heights[i++] - heights[i];            
        }   
        total+=difference;   
      }   
   return total;   
 }

Answer 1

你在循环中增加i，因此可能超出范围：

for(int i=start;i<=end;i++){      // here i might be last valid index, i.e. 4 in your example     
    if(heights[i] > heights[i++]){    //here i might be 5 (because of i++), i.e. you'd get the ArrayIndexOutOfBoundsException     
       difference =heights[i] - heights[i++]; //here i might be 6 (because of another i++), i.e. you'd get the ArrayIndexOutOfBoundsException                 
    }else if(heights[i++] > heights[i]){     //here i might be 5, i.e. you'd get the ArrayIndexOutOfBoundsException    
       difference =heights[i++] - heights[i];            
    }   
    total+=difference;   
  }

要解决此问题，请使用：

for(int i=start;i<end;i++){   
int next = i + 1;     
    if(heights[i] > heights[next]){  
       difference =heights[i] - heights[next]; //assuming you mean next = i + 1 here and not next = i + 2 like in your code               
    }else if(heights[next] > heights[i]){    
       difference =heights[next] - heights[i];            
    }   
    else {
      difference = 0; //due to public demand I'll help you with this, too
    }

    total+=difference;   
  }

编辑：您还可以使循环更简单：

for(int i=start;i<end;i++){   
  total += Math.abs(heights[i] - heights[i+1]);  
}

Answer 2

这是因为

在循环内增加变量i。在循环中使用i+1代替i++。 ++运算符不返回i+1，而是返回i并指定i=i+1。
另一个问题是，for循环对i的值定义错误。如果你想返回sumHeights({11, 12}, 0, 1)，你想要只运行一次循环吗？如果你运行这个循环两次i+1将在第二次运行中等于2，它将使索引超出绑定异常。
另一个问题是heights[i] == heights[i+1] - 在这种情况下，不会重新计算差异，并且可能会在之前的循环运行中分配。您可以通过在循环内移动difference变量声明来解决它。

试试这段代码：

 public int sumHeights(int[] heights, int start, int end) {        

   int total =0;   
      for(int i=start;i<end;i++){           
        int difference =0;   
        if(heights[i] > heights[i+1]){         
           difference =heights[i] - heights[i+1];          
        }else if(heights[i+1] > heights[i]){         
           difference =heights[i+1] - heights[i];            
        }   
        total+=difference;   
      }   
   return total;   
 }

Answer 3

我是这样做的：

 public int sumHeights(int[] heights, int start, int end) {
 int sum=0;
while(start<end)
 {
   sum+=Math.abs(heights[start+1]-heights[start]);
   start++;
 }
return sum;
}

找出步行道的距离之间的高度

3 个答案: