42

题目

方法一：集合法

var trap = function(height) {
  const stack=[]
  let i=0,ans=0
  while(i<height.length){
    while(stack.length!==0&&height[i]>height[stack[stack.length-1]]){
      let top=height.pop()
      if(stack.length===0)break;
      let distance=i-stack[stack.length-1]-1
      let height2=Math.min(height[i],height[stack[stack.length-1]]-height[top])
      console.log(distance,height2);
      ans+=distance * height2
    }
    stack.push(i++)
  }
  return ans
};

方法二：栈