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@@ -0,0 +1,58 @@
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+class Solution {
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+ // Numbers 0-9
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+ // Exponent - "e"
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+ // Positive/negative sign - "+"/"-"
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+ // Decimal point - "."
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+ public boolean isNumber(String s) {
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+ // Finite automaton
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+ // State No. | Discription
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+ // -1 | Invalid state
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+ // 0 | Initail state
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+ // 1 | Input sign
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+ // 2 | Input digit
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+ // 3 | Input dot
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+ // 4 | Input digit and dot
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+ // 5 | Input exp
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+ // 6 | Input sign after exp
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+ // 7 | Input digit after exp
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+ // 8 | Input space after valid number
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+ // Input state:
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+ // INVALID, SPACE, SIGN, DIGIT, DOT, EXP
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+ // Trans table:
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+ // input ERR SPA SGN DIG DOT EXP
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+ // state
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+ // 0 -1 0 1 2 3 -1
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+ // 1 -1 -1 -1 2 3 -1
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+ // 2 -1 8 -1 2 3 5
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+ // 3 -1 -1 -1 4 -1 5
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+ // 4 -1 8 -1 4 -1 5
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+ // 5 -1 -1 6 7 -1 -1
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+ // 6 -1 -1 -1 7 -1 -1
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+ // 7 -1 8 -1 7 -1 -1
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+ // 8 -1 8 -1 -1 -1 -1
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+ char[] num = s.toCharArray();
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+ int[][] stateTable = new int[][] {
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+ {-1, 0, 1, 2, 3, -1}, // 0
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+ {-1, -1, -1, 2, 3, -1}, // 1
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+ {-1, 8, -1, 2, 4, 5}, // 2
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+ {-1, -1, -1, 4, -1, -1}, // 3
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+ {-1, 8, -1, 4, -1, 5}, // 4
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+ {-1, -1, 6, 7, -1, -1}, // 5
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+ {-1, -1, -1, 7, -1, -1}, // 6
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+ {-1, 8, -1, 7, -1, -1}, // 7
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+ {-1, 8, -1, -1, -1, -1} // 8
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+ };
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+ int state = 0;
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+ for (int i = 0; i < num.length; i++) {
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+ int input = 0;
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+ if (num[i] == ' ') input = 1;
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+ else if (num[i] == '+' || num[i] == '-') input = 2;
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+ else if ('0' <= num[i] && num[i] <= '9') input = 3;
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+ else if (num[i] == '.') input = 4;
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+ else if (num[i] == 'e' || num[i] == 'E') input = 5;
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+ state = stateTable[state][input];
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+ if (state == -1) return false;
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+ }
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+ return state == 2 || state == 4 || state == 7 || state == 8;
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+ }
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+}
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