/**
 * @param {number[]} height
 * @return {number}
 */
var trap = function (height) {
  let len = height.length;
  let pre_max = new Array(len).fill(0);
  let suf_max = new Array(len).fill(0);

  pre_max[0] = height[0];
  suf_max[len - 1] = height[len - 1];

  for (let i = 1; i < len; i++) {
    pre_max[i] = Math.max(pre_max[i - 1], height[i]);
  }

  for (let j = len - 2; j >= 0; j--) {
    suf_max[j] = Math.max(suf_max[j + 1], height[j]);
  }

  let ans = 0;
  for(let k = 0;k<len;k++){
    let h = height[k];
    let pre = pre_max[k]
    let suf = suf_max[k];

    ans +=(Math.min(pre,suf)-h)
  }

  return ans;
};

console.log(trap([0,1,0,2,1,0,1,3,2,1,2,1]))
console.log(trap([4,2,0,3,2,5]))

执行用时分布
63ms
击败69.22%使用 JavaScript 的用户

消耗内存分布
54.13MB
击败15.49%使用 JavaScript 的用户

class Solution:
    def trap (self, height: List[int])->int:
        n = len(height)
        pre_max = [0]*n
        pre_max[0] = height[0]
        suf_max = [0]*n
        suf_max[-1] = height[-1]
    
        for i in range(1,n):
            pre_max[i]=max(pre_max[i-1],height[i])
        
        for i in range(len-2,-1,-1):
            suf_max[i] = max(suf_max[i+1],height[i])

        ans = 0
        for h,pre,suf in zip(height,pre_max,suf_max):
            ans+=min(pre,suf)-h

        return ans

• 优化空间复杂度O(1)

/**
 * @param {number[]} height
 * @return {number}
 */
var trap = function(height) {
  let len = height.length;
  let left = 0,right = len-1;

  let pre_max = 0,suf_max = 0;
  let ans = 0;
  while(left<=right){
    pre_max = Math.max(pre_max,height[left])
    suf_max = Math.max(suf_max,height[right])

    if(pre_max<suf_max){
        ans += pre_max-height[left]
        left++
    }else{
        ans += suf_max-height[right]
        right--
    }
  }

  return ans;
};

执行用时分布
46ms 击败99.34%
使用 JavaScript 的用户

消耗内存分布
49.84MB击败98.37%
使用 JavaScript 的用户