42. 接雨水

test007.cpp

@@ -0,0 +1,31 @@
+class Solution {
+public:
+    int trap(vector<int>& h) {
+        int n = h.size();
+        using pii = pair<int, int>;
+        using ll = long long;
+        stack<pii> stk;
+
+        int ret = 0;
+        for(int i = 0; i < n; i++){
+            ll sum = 0;
+            ll W = 0;
+            int lastH = 0;
+
+            while(!stk.empty() && stk.top().second < h[i]){
+                lastH = stk.top().second;
+                W += stk.top().first;
+                sum += 1LL * stk.top().first * stk.top().second;
+                stk.pop();
+            }
+            if(stk.empty()){
+                ret += W * lastH - sum;
+                stk.push({1, h[i]});
+            }else{
+                ret += W * h[i] - sum;
+                stk.push({W + 1, h[i]});
+            }
+        }
+        return ret;
+    }
+};