EPI: power_x_y (CPP/Py)

Author: jsgoller1

elements-of-programming-interviews/cpp/power_x_y.cc

@@ -1,7 +1,21 @@
 #include "test_framework/generic_test.h"
+double _helper(double x, int y, std::map<int, double>& dp) {
+  if (dp.find(y) != dp.end()) {
+    return dp[y];
+  }
+  double val = _helper(x, y / 2, dp);
+  val *= val;
+  if (y % 2) {
+    val = (y < 0) ? val / x : val * x;
+  }
+  dp[y] = val;
+  return dp[y];
+}
+
 double Power(double x, int y) {
-  // TODO - you fill in here.
-  return 0.0;
+  std::map<int, double> dp{{0, 1}, {1, x}, {-1, (1.0 / x)}};
+  _helper(x, y, dp);
+  return dp[y];
 }
 
 int main(int argc, char* argv[]) {

elements-of-programming-interviews/problem_mapping.js

@@ -100,15 +100,15 @@ problem_mapping = {
         },
         "4.07 Compute pow(x,y)": {
             "C++: power_x_y.cc": {
-                "passed": 0,
+                "passed": 10002,
                 "total": 10002
             },
             "Java: PowerXY.java": {
                 "passed": 0,
                 "total": 10002
             },
             "Python: power_x_y.py": {
-                "passed": 0,
+                "passed": 10002,
                 "total": 10002
             }
         },

elements-of-programming-interviews/python/power_x_y.py

@@ -1,11 +1,36 @@
 from test_framework import generic_test
 
 
+def brute_force_power(x: float, y: int) -> float:
+    total = 1.0
+    if y >= 0:
+        for i in range(1, y+1):
+            total *= x
+    else:
+        for i in range(1, (-y)+1):
+            total /= x
+    return total
+
+
+def _helper(x: float, y: int, dp: dict) -> float:
+    if y in dp:
+        return dp[y]
+    val = _helper(x, y//2, dp) * _helper(x, y//2, dp)
+    if y % 2:   # odd
+        val = (val * x)
+    dp[y] = val
+    return dp[y]
+
+
 def power(x: float, y: int) -> float:
-    # TODO - you fill in here.
-    return 0.0
+    dp = {
+        0: 1.0,
+        1: x,
+        -1: (1/x)
+    }
+    _helper(x, y, dp)
+    return dp[y]
 
 
 if __name__ == '__main__':
-    exit(generic_test.generic_test_main('power_x_y.py', 'power_x_y.tsv',
-                                        power))
+    exit(generic_test.generic_test_main('power_x_y.py', 'power_x_y.tsv', power))