力扣算法题—042接雨水

  1 #include"000库函数.h"
  2 //一点头绪都没有
  3 //然后就自己按自己的意思来一遍
  4 //好像没有用算法
  5 //16ms,让我激动一把
  6
  7 class Solution {
  8 public:
  9     int trap(vector<int>& height) {
 10         if (height.size() < 2)return 0;
 11         int s = 0;//起始点
 12         int e = 0;//终止点
 13         int v = 0;//接雨水量
 14         int t = 0;//计算中间掠过的柱子
 15         int i, j;
 16         for (i = 0; i < height.size()-1; ++i) {
 17             if (height[i] < 1)continue;
 18             s = height[i];//找到非0点为起始点
 19             for (j = i + 1; j < height.size(); ++j) {
 20                 if (height[j] >= s) {//找到比起始点大或者相等的点
 21                     e = height[j];
 22                     break;
 23                 }
 24                 t += height[j];
 25                 if (j == height.size() - 1) {//没有比起始点小的数了
 26                     --s;//对s进行降高度
 27                     j = i;//重新遍历
 28                     t = 0;//重新计算中间掠过的柱子
 29                 }
 30             }
 31             v += (s < e ? s : e)*(j - i - 1) - t;//计算体积，记得减去中间的掠过体积
 32             t = 0;//下一步重新计算掠过的体积
 33             i = j - 1;//换过起始点（即终止点作为新的起始点）
 34         }
 35         return v;
 36     }
 37 };
 38
 39 //下面是看够力扣题解之后的答案
 40 //根据力扣上面的解题提示
 41 //尝试着做一下
 42 //使用暴力法进行解答
 43 //484ms
 44 class Solution {
 45 public:
 46     int trap(vector<int>& height) {
 47         int ans = 0;
 48         int size = height.size();
 49         for (int i = 1; i < size - 1; i++) {
 50             int max_left = 0, max_right = 0;
 51             for (int j = i; j >= 0; j--) { //Search the left part for max bar size
 52                 max_left = max(max_left, height[j]);
 53             }
 54             for (int j = i; j < size; j++) { //Search the right part for max bar size
 55                 max_right = max(max_right, height[j]);
 56             }
 57             ans += min(max_left, max_right) - height[i];
 58         }
 59         return ans;
 60     }
 61 };
 62 //
 63 //
 64 //使用动态规划20ms
 65 //
 66 class Solution {
 67 public:
 68     int trap(vector<int>& height) {
 69         if (height.size() == NULL)return 0;
 70         int ans = 0;
 71         int size = height.size();
 72         vector<int> left_max(size), right_max(size);
 73         left_max[0] = height[0];
 74         for (int i = 1; i < size; i++) {
 75             left_max[i] = max(height[i], left_max[i - 1]);
 76         }
 77         right_max[size - 1] = height[size - 1];
 78         for (int i = size - 2; i >= 0; i--) {
 79             right_max[i] = max(height[i], right_max[i + 1]);
 80         }
 81         for (int i = 1; i < size - 1; i++) {
 82             ans += min(left_max[i], right_max[i]) - height[i];
 83         }
 84         return ans;
 85     }
 86 };
 87 //
 88 //
 89 //使用堆栈法28ms
 90 //
 91 class Solution {
 92 public:
 93     int trap(vector<int>& height) {
 94         int ans = 0, current = 0;
 95         stack<int> st;
 96         while (current < height.size()) {
 97             while (!st.empty() && height[current] > height[st.top()]) {
 98                 int top = st.top();
 99                 st.pop();
100                 if (st.empty())
101                     break;
102                 int distance = current - st.top() - 1;
103                 int bounded_height = min(height[current], height[st.top()]) - height[top];
104                 ans += distance * bounded_height;
105             }
106             st.push(current++);
107         }
108         return ans;
109     }
110 };
111 //
112 //使用双指针法16ms
113 //
114 class Solution {
115 public:
116     int trap(vector<int>& height) {
117         int left = 0, right = height.size() - 1;
118         int ans = 0;
119         int left_max = 0, right_max = 0;
120         while (left < right) {
121             if (height[left] < height[right]) {
122                 height[left] >= left_max ? (left_max = height[left]) : ans += (left_max - height[left]);
123                 ++left;
124             }
125             else {
126                 height[right] >= right_max ? (right_max = height[right]) : ans += (right_max - height[right]);
127                 --right;
128             }
129         }
130         return ans;
131     }
132 };
133
134
135 void T042() {
136     Solution s;
137     vector<int>v;
138     v = { 0,1,0,2,1,0,1,3,2,1,2,1 };
139     cout << s.trap(v) << endl;
140     v = { 4,2,1,2,4 };
141     cout << s.trap(v) << endl;
142     v = { 0,4,0,3,0,2};
143     cout << s.trap(v) << endl;
144
145
146 }

原文地址：https://www.cnblogs.com/zzw1024/p/10578399.html