add prob #844; O(N) in time and O(1) in space;

Author: randomwalk10

844_Backspace_String_Compare_2nd.cpp

@@ -0,0 +1,34 @@
+/* O(N) in time and O(1) in space */
+#include <string>
+using namespace std;
+
+class Solution {
+public:
+    bool backspaceCompare(string S, string T) {
+        int i = S.size() - 1;
+        int j = T.size() - 1;
+        while(true){
+            int bcnt = 0;
+            while( (i>=0)&&( (S[i]=='#')||(bcnt>0) ) ){
+                if(S[i]=='#') ++bcnt;
+                else --bcnt;
+                --i;
+            }
+            bcnt = 0;
+            while( (j>=0)&&( (T[j]=='#')||(bcnt>0) ) ){
+                if(T[j]=='#') ++bcnt;
+                else --bcnt;
+                --j;
+            }
+
+            if( (i<0)&&(j<0) ) break;
+            else if(i<0) return false;
+            else if(j<0) return false;
+            else if(S[i]==T[j]){
+                --i; --j;
+            }
+            else return false;
+        }
+        return true;
+    }
+};