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63 lines (56 loc) · 1.79 KB
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/**
* Creates range minimum query structure
* @class RMQ
*
* @param {number[]} items Collection of numbers
* @returns {RMQ} Returns range minimum query structure
*/
export default function RMQ(items) {
var _lookup = [];
var _log2 = Math.log(2);
preprocess();
function preprocess() {
var power;
for (var index = 0, len = items.length; index < len; index += 1) {
_lookup[index] = [index];
}
for (power = 1, len = items.length; (1 << power) < len; power += 1) {
for (index = 0; (index + (1 << power) - 1) < len; index += 1) {
if (items[_lookup[index][power - 1]] < items[_lookup[index + (1 << (power - 1))][power - 1]]) {
_lookup[index][power] = _lookup[index][power - 1];
} else {
_lookup[index][power] = _lookup[index + (1 << (power - 1))][power - 1];
}
}
}
}
/**
* Returns index of minimum item for the given range of items
*
* @param {number} from The left margin index
* @param {number} to The right margin index
* @returns {number} Returns index of the minimum item
*/
function getRangeMinimumIndex(from, to) {
var power = Math.floor(Math.log(to - from + 1) / _log2);
if (items[_lookup[from][power]] <= items[_lookup[to - (1 << power) + 1][power]]) {
return _lookup[from][power];
} else {
return _lookup[to - (1 << power) + 1][power];
}
}
/**
* Return minimum value for the given range
*
* @param {number} from The left index of the range
* @param {number} to The right index of the range
* @returns {number} Returns minimum value in the range
*/
function getRangeMinimum(from, to) {
return items[getRangeMinimumIndex(from, to)];
}
return {
getRangeMinimumIndex: getRangeMinimumIndex,
getRangeMinimum: getRangeMinimum
};
};