Solve the equation "1 2 3 4 5 6 7 8 9 = 100" by putting in only adds and takes. Requires a div with id "result" on the page to work.

fp-2011-02-04.js

    var calc = function() {

        var coefficients = [1, 2, 3, 4, 5, 6, 7, 8, 9],
            signTable = ['-', '', '+'],
            cases = 0,
            caseFormula = '',
            ternary = '',
            i = 0,
            result = {},
            r = document.getElementById('result'),

            toTernary = function(n) {
                var s = '', b = 3;

                n = parseInt(n, 10);
                while(n >= b) {
                    s = (n % b) + s;
                    n = Math.floor(n/b);
                }
                return ((n != 0 ? n : '') + s);
            },

            pad = function(s) {
                var i, add = coefficients.length - s.length;

                for(i = 0; i < add; i++) {
                    s = '0' + s;
                }
                return s;
            },

            evaluate = function(s) {
                var sign = 1, values = [], i, result = 0;
                for(i = 0; i < s.length; i++) {
                    switch(s[i]) {
                        case '+':
                            result += sign*values.join('');
                            sign = 1;
                            values = [];
                            break;
                        case '-':
                            result += sign*values.join('');
                            sign = -1;
                            values = [];
                            break;
                        default:
                            values.push(s[i]);
                    }
                }
                return result + sign*values.join('');
            };

            for(cases = 0; cases < 19683; cases++) {
                caseFormula = '';
                ternary = pad(toTernary(cases));
                for(i = 0; i < coefficients.length; i++) {
                    caseFormula += signTable[parseInt(ternary[coefficients.length-i-1])] + coefficients[i];
                }
                if(100 == evaluate(caseFormula)) {
                    result[caseFormula] = 0;
                }
            }

            cases = 0;
            for(i in result) {
                if(100 == eval(i)) {
                    r.innerHTML += i + ' = 100<br /' + '>';
                    cases++;
                }
            }

            r.innerHTML += '<br /' + '>Found ' + cases + ' solutions.';

    };