Difference between revisions of "CSC212 Final Exam 2014"
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=Problem #9= | =Problem #9= | ||
| − | * | + | * Assume we have a function that generates random RPN expressions: |
| + | <source lang="java"> | ||
| + | static String randomRPN( int n ) { | ||
| + | Random generator = new Random(); | ||
| + | generator.setSeed( 11 ); | ||
| + | String s = ""; | ||
| + | int noOps = 0; | ||
| + | int no11s = 0; | ||
| + | for ( int i=0; i<n; i++ ) { | ||
| + | int r = generator.nextInt(5); | ||
| + | int x =(1+generator.nextInt(10)); | ||
| + | int y =(1+generator.nextInt(10)); | ||
| + | switch ( r ) { | ||
| + | case 0: s += x + " " + y + " + "; noOps++; break; | ||
| + | case 1: s += x + " " + y + " - "; noOps++; break; | ||
| + | case 2: s += x + " " + y + " % "; noOps++; break; | ||
| + | case 3: s += "11 "; no11s++; break; | ||
| + | } | ||
| + | } | ||
| + | noOps--; | ||
| + | while ( noOps-- > 0 ) | ||
| + | s += "+ "; | ||
| + | while ( no11s-- > 0 ) | ||
| + | s += "- "; | ||
| + | return s; | ||
| + | } | ||
| + | </source> | ||
| + | * If we call it and pass it 200 as an argument, it prints a fairly long string, starting with "11 4 8 + 4 4 + 5 5 %" and ends with " - - - - - - - - - -". | ||
| + | * If we evaluate this RPN expression, the result is -725. True of False? | ||
| + | :(answer: False, it's -726) | ||
</onlydft> | </onlydft> | ||
