<p>Describe how you could use a single array to implement three stacks.</p> <p>You should implement <code>push(stackNum, value)</code>、<code>pop(stackNum)</code>、<code>isEmpty(stackNum)</code>、<code>peek(stackNum)</code> methods. <code>stackNum<font face="sans-serif, Arial, Verdana, Trebuchet MS"> </font></code><font face="sans-serif, Arial, Verdana, Trebuchet MS">is the index of the stack. </font><code>value</code> is the value that pushed to the stack.</p> <p>The constructor requires a <code>stackSize</code> parameter, which represents the size of each stack.</p> <p><strong>Example1:</strong></p> <pre> <strong> Input</strong>: ["TripleInOne", "push", "push", "pop", "pop", "pop", "isEmpty"] [[1], [0, 1], [0, 2], [0], [0], [0], [0]] <strong> Output</strong>: [null, null, null, 1, -1, -1, true] <b>Explanation</b>: When the stack is empty, `pop, peek` return -1. When the stack is full, `push` does nothing. </pre> <p><strong>Example2:</strong></p> <pre> <strong> Input</strong>: ["TripleInOne", "push", "push", "push", "pop", "pop", "pop", "peek"] [[2], [0, 1], [0, 2], [0, 3], [0], [0], [0], [0]] <strong> Output</strong>: [null, null, null, null, 2, 1, -1, -1] </pre>