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0042.trapping_rain_water.cpp
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0042.trapping_rain_water.cpp
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#include <iostream>
#include <vector>
using std::vector;
// 可以发现朴素方法需要三次遍历
// 一次找左边最大,一次找右边最大,一次计算
// 但实际上,只需要一次即可
int trap(vector<int>& h)
{
int n = h.size();
int l = 0, r = n - 1;
int ml = 0, mr = 0;
int res = 0;
while (l < r) {
ml = std::max(ml, h[l]);
mr = std::max(mr, h[r]);
if (h[l] < h[r]) {
res += ml - h[l];
++l;
} else {
res += mr - h[r];
--r;
}
}
return res;
}
// 朴素的思想是找到左右最大高度
// 那么两者中较小的减去当前高度,即为当前可接雨水
int _trap(vector<int>& h)
{
int n = h.size();
vector<int> l(n, 0), r(n, 0);
l[0] = h[0], r[n-1] = h[n-1];
for (int i = 1; i < n; ++i) {
l[i] = std::max(l[i-1], h[i]);
}
for (int i = n - 2; i >= 0; --i) {
r[i] = std::max(r[i+1], h[i]);
}
int res = 0;
for (int i = 0; i < n; ++i) {
res += std::min(l[i], r[i]) - h[i];
}
return res;
}
int main () {
#ifdef LOCAL
freopen("0042.in", "r", stdin);
#endif
int n = 0;
while (std::cin >> n) {
vector<int> h(n);
for (int i = 0; i < n; ++i) {
std::cin >> h[i];
}
std::cout << trap(h) << std::endl;
}
return 0;
}