数组-接雨水

    const elevationArray = [0,1, 0,2, 1,0,3,1,0,1,2]
    const getTrappedRainwater =  function(heights){
        let totalWater = 0;
        for(let p = 0;p<heights.length;p++){
            let leftP = p,rightP = p,maxLeft = 0,maxRgith  =0;
            while(leftP>=0){
                maxLeft = Math.max(heights[leftP],maxLeft)
                leftP--
            }
            while(rightP<heights.length){
                maxRgith = Math.max(heights[rightP],maxRight)
                rightP++
            }
            const currentWater = Math.min(maxLeft,maxRgith) - heights[p]
            if(currentWater >= 0){
                totalWater += currentWater
            }
        }

    }

    const getTrappedRainwater = function(heights){
        let left = 0,
            right  = heights.length -1,
            totalWater = 0,
            maxLeft = 0,
            maxRgith = 0;
        while(left<right){
            if(heights[left]<=heights[right]){
                if(heights[left] >= maxLeft){
                    maxLeft = heights[left]
                }else{
                    totalWater += maxLeft - heights[left]           
                }
                left++
            }else{
                if(heights[right] >= maxRight){
                    maxRight = heights[right]
                }else{
                    totalWater += maxRgith - heights[right]
                }
                right--
            }
        }
    }