問題描寫

Given n non-negative integers a1, a2, …, an, where each represents a point at coordinate (i, ai). n vertical lines are drawn such that the two endpoints of line i is at (i, ai) and (i, 0). Find two lines, which together with x-axis forms a container, such that the container contains the most water.

水桶裝水求容積，實際上是求各條線組成的長方形的面積。

問題分析

保存左右兩個指針，每次計算出當前長方形的面積（高是短的那條線，寬是兩個指針的距離），然后與當前最大值進行比較，如果大于當前最大值就替換掉；然后比較兩個指針指向的值，移動值小的指針，即移動決定高的。

可以理解為最開始就把寬設為最大，然后不斷縮小寬，增長高。

代碼

class Solution {
public:
    int maxArea(vector<int>& height) {
        if(height.size()<=1) return 0;
        int left=0;
        int right = height.size()-1;
        int max_area = 0;
        while(left<right) {
            max_area = max(max_area, 
                min(height[left],height[right])*(right-left));
            if(height[left]>=height[right]) {
                right--;
            } else {
                left++;
            }
        }
        return max_area;
    }
};